Focussing on the interactive nuances in this way often requires a shift in perspective as to what is a figure and what is ground. For example, where a patient drifts into a fantasy that figuratively takes him or her out of the room, perhaps the affirmation to what is in Latin projectio, yet the interactive meaning is as important as the actual content (if not more so). Exploring what triggered the fantasy, and what its immediate interactive function might be, may help the patient grasp some of the subtler patterns of his or her own experiential flame, inasmuch as to grasp to its thought. While the content of the fantasy can provide useful clues to its distributive contribution of its dynamical function, staying with content may be a way for both patient and analyst to collude in avoiding engaging the anxieties of the moment.
Where some form of collusion does occur, as at times it inevitably will, demystifying the collusion has internal repercussions as well. The clarification of patterns of self-mystification (Laing 1965) that this makes it a possibly that being often liberating. It can facilitate a shift on the part of the patient from feeling victimized or helpless, stuck without any options, too freshly experiencing his or her own power and responsibility in relation to multiple choices.
For example, one patient who had difficulty defining where she ended and the other began was invariable in a constant state of anger with others for what she perceived as their not allowing her feelings, as how this operated between us, she realized that no one could control her feelings and that it was her inordinate need for the approval of others that were controlling her. It was her need to control the other, to control the other’s reaction to her, that was defining her experience. The result was that she began to feel less threatened and paranoid. She also was able to begin to deal analytically with the unconscious dynamics of her needs for approval and for control, and to focus on her anxieties in a way not possibly earlier.
We must then, ask of ourselves, are the afforded efforts to control the given as the ‘chance’ to ‘change’, or the given ‘change’ to ‘chance’? As a neutral type of the therapist participation proves to be essential to the resolution of the schizophrenic patient’s basic ambivalence concerning individuation - his intense conflict, that is, between clinging and a hallucinatory, symbiotic mode of existence, in which he is his whole perceived world, or on the other hand relinquishing this mode of experience and committing himself to object-relatedness and individuality - too becoming, that is, a separate person in a world of other persons. Will (1961) points out that just as ‘In the moves toward closeness the person finds the needed relatedness and identification with another, in the withdrawal (often marked by negativism) he finds the separateness that favours his feelings of being distinct and self-identified, and Burton (1961) says that “In the treatment, the patient’s desire for privacy is respected and no encroachment is made. The two conflicting needs war with each other and it is a serious mistake for the therapist to take sides too early.” The schizophrenic patient has not as to the experience that commitment too object-relatedness still allows for separateness and privacy, and where Séchehaye (1956) recommends that one “make oneself a substitute for the autistic universe that helped to offer as of a given choice that must rest in the patient’s hands.” This regarded primeval area of applicability of a general comment by Burton (1961) that ”In the psychotherapy of every schizophrenic a point is reached where the patient must be confronted with his choice. . . .” Of Shlien’s (1961) comment that “Freedom means the widest scope of choice and openness to experience . . . .”
Only in a therapeutic setting where he finds the freedom to experience both these modes of relatedness with one and the same person can the patient become able to choose between psychosis and emotional maturity. He can settle for this later only in proportion as he realizes that both object-relatedness and symbiosis are essential ingredients of healthy human relatedness - that the choice between these modes amounts not to a once-for-all commitment, but that, to enjoy the gratification of human relatedness he must commit himself to either object-relatedness or symbiotic relatedness, as the chancing needs and possibilities that the basic therapeutics requires and permit.
Such, as to say, the problem is to reconcile our everyday consciousness of us as agents, with the best view of what science tells us that we are. Determinism is one part of the problem. It may be defined as the doctrine that every event has a cause. More precisely, for any event as ‘e’, there will be some antecedent state of nature ‘N’, and a law of nature. ‘L’, such that given to ‘L’, ‘N’, will be followed by 'e'. Yet if this is true of every event, it is true of events such as my doing something or choosing to do something. So my choosing or doing something is fixed by some antecedent state ‘N’ and the laws. Since determinism is universal these in turn are fixed, and so backwards to events, for which I am clearly not responsible (events before my birth, for example). So no events can be voluntary or free, where that means that they come about purely because of free willing them, as when I could have done otherwise. If determinism is true, then there will be antecedent states and laws already determining such events? : How then can I truly be said to be their author, or be responsible for them? Reactions to this problem are commonly classified as: (1) hard determinism. This accepts the conflict and denies that you have real freedom or responsibility. (2) Soft determinism or compatibility. Reactions in this family assert that everything you should want from a notion of freedom is quite compatible with determinism. In particular, even if your action is caused, it can often be true of you that you could have done otherwise if you had chosen, and this may be enough to render you liable to be held responsible or to be blamed if what you did was unacceptable (the fact that previous events will have caused you to choose as doing so and deemed irrelevant on this option). (3) Libertarianism. This is the view that, while compatibilism is inly an evasion, there is a more substantive, real notion of freedom that can yet be preserved in the face of determinism (or of in determinism). While the empirical or phenomenal self is determined and not free, the noumenal or rational self is capable of rational, free action. Nevertheless, since the noumenal self exists outside the categories of space and time, this freedom seems to be of doubtful value. Other libertarian avenues include suggesting that the problem is badly framed, for instance because the definition of determinism breaks down, or postulating a special category of uncaused acts of volition, or suggesting that there are two independent but consistent ways of looking at an agent, the scientific and humanistic. It is only through confusing them that the problem seems urgent. None of these avenues accede to exist by a greater than is less to quantities that seem as not regainfully to employ to any inclusion nontechnical ties. It is an error to confuse determinism and fatalism. Such that, the crux is whether choice, is a process in which different desires, pressures, and attitudes fight it out and eventually result in one decision and action, or whether in attitudinal assertions that there is a ‘self’ controlling the conflict, in the name of higher desires, reasons, or mortality? The attempt to add such a extra to the more passive picture (often attributed to Hume), and is a particular target not only of Humean, but also of much feminist and postmodernist writing.
Thus and so, the doctrine that every event has a cause infers to determinism. The usual explanation of this is that for every event, there is some antecedent state, related in such a way that it would break a law of nature for this antecedent state to exist, and as yet the event not to happen. This is a purely metaphysical claim, and carries no implications for whether we can in a principal product the event. The main interest in determinism has been in asserting its implications for ‘free will’. However, quantum physics is essentially indeterministic, yet the view that our actions are subject to quantum indeterminacies hardly encourages a sense of our own responsibility for them.
As such, these reflections are simulated by what might be regarded as naive surprise at the impact of the renewed emphasis on the ‘here-and-now’ in our technical work during the last few years, including the early interpretations of the transference. This emphasis has been argued most vigorously by Gill and Muslin (1976) and Gill (1979). It has at times been reacting to, as if it were a technical innovation, and, of course, making it clear, all the same, from the persistence and reiteration that characterize Gill’s contributions, that he believes the “resistance to the awareness of transference” to be a critically important and neglected area in psychoanalytic work, this may deserve further emphasis. In Gill’s latest contribution of which as before, he concedes that the recall or reconstruction of the past remains useful but that the working out of conflict in the current transference is the more important, i.e., should have priority of attention. In view of the centrality of issues and its interesting place in the development of psychoanalysis, the contributory works of Gill and Muslin (1976). Gill (1979) presents a subtle and searching review and analysis of Freud’s evolving views on the interrelationship between the conjoint problems of transference and resistance and the indications for interpretation. Repeating this painstaking work would therefore be superfluous. Our’s is for a final purpose to state for reason to posit of itself upon the transference and non-transference interpretation and beyond this, to sketch a tentative certainty to the implications and potentialities of the ‘here-and-now’.
In a sense, the current emphasis may be the historical ‘peaking’ of a long and gradual, if fluctuating, development in the history of psychoanalysis. We know that Freud’s first re-counted with the transference, the ‘false connection’, was its role as a resistance (Breuer and Freud 1893-1895). While Freud’s view of this complex phenomenon soon came to include its powerfully affirmative role in the psychoanalytic process, the basis importance of the ‘transference resistance’ remained. In the Dynamics of Transference (1912) stated in dramatic figurative terms the indispensable current functions of the transference: “For when all is said and done, destroying anyone in absentia or in effigies is impossible.” In fact, to some of us, the two manifestly opposing forces are two sides of the same coin. As, perhaps, the relationship is eve n more intimate, in the sense that the resistance is mobilized in the first place b the existence of (manifest or - often - latent) transference. It is spontaneous protective reaction against loss of love, or punishment, or narcissistic suffering in the unconscious infantile context of the process.
Historically, the effective reinstatement of his personal past into the patient’s mental life was thought to be the essential therapeutic vehicle of analysis and thus its operational goal. This was, of course, modified with time, explicitly or in widespread general understanding. The recollection or reconstruction of an experience, however critical its importance, evidently did not (except in relatively few instances) immediately dissolve the imposing edifice of structuralized reaction patterns to which it may have importantly y contributed, this (dissolution) might indeed occur - dramatically - in the case of relatively isolated, encapsulated, and traumatic experiences, but only rarely y in the chronic psychoneuroses whose genesis was usually different and far more complex. Freud’s (1914) discovery of the process of ‘working through’, along with the emphasis on its importance, was one manifestation of a major process of recognition of the complexity, persuasiveness, and tenacity of the current dynamics of personality, in relation to both genetic and dynamic factors of early or origin. Perhaps Freud’s (1937) most vivid figurative recognition of the pseudoparadoxical role of early genetic factors, If not understood as part of a complex continuum, was in his “lamp-fire” critique of the technical implications of Rank’s (1924) Trauma of Birth. The term pseudoparadoxical is used because the recovery of the past by recollection or reconstruction - if no longer the sole operational vehicle and goal of psychoanalysis - retains a unique intimate and individual explanatory value, essential to genuine insight into the fundamental issues of personality development and distortion.
When Ferenczi and Rank wrote The Development of Psychoanalysis in 1924, they proposed an enormous emphasis on emotional experience in the analytic process, as opposed to what was thought to be the effectively sterile intellectual investigation the n in vogue. Instead of the speedy reduction of disturbing transference experience by interpretation, these authors, in a sense, advised the elucidation and cultivation of emotional intensities. (As Alexander pointed out in 1925, however, the method was not clear.) These alone could lend a vivid sense of reality and meaningfulness to the basic dynamism of personality incorporated in the transference. Now it is to be masted and marked that in this work, too, there is no ‘repudiation’ of the past. Ultimately genetic interpretations were to be made. The intense transference experience, as mentioned, was intended to give body, reality, to the living past. Yet, the ultimate significance of construction was invoked, in the sense of ‘supplying’ those memories that might not be spontaneously available. It was felt that the crucial experiences of childhood had usually been promptly repressed and thus not experiences in consciousness in any significant degree. Therapeutic effectiveness of the process was attributed largely to the intensity of emotional experience, than to the depth and ramifications of detained cognitive insight. The fostering in of transference intensity, as, we can infer, was rather by withholding or scantiness of interpretations (as opposed to making facilitating interpretations) and, at times (as specifically stared), by mild confirming responses or attitudes in the affective sphere: These would tend to support the patient’s transference affects in interpersonal reality (Ferenczi and Rank 1024).
This is, of course, different from the recent emphasis on ‘early interpretation of the transference (Gill and Muslin 1976), which in a process in the cognitive sphere designed to overcome resistance to awareness of transference and thuds to mobilize the latter as an active participant in the analysis as soon as possible. What they have in common is an undeniable emphasis on current experience, explicitly in the transference. Also, in both tendencies there is an implicit minimization of the vast and rich territories of mind and feeling, which may become available and at times uniquely informative if fewer tendentious attitudes govern the analyst’s initial approach. Correspondingly, in both there is the hazard of stimulating resistance of a stubborn, well-rationalized maturity by the sheer tendentious of approachment, and similarly transference tendency pursued assiduously by the analyst.
The question of the moments entering a sense of conviction in the patient (a dynamically indispensable state) is, of course, a complex matter. However, if one is to think that few would doubt that immediate or closely proximal experience (‘today’ or ‘yesterday’) occasions grater vividness and sense of certainty than isolated recollection or reconstruction of the remote past. Thus the “here-and-now” in analytic work, the immediate cognitive exchange and the important current emotional experiences, and, under favourable conditions, contributes to other elements in the process, i.e., recovery or reconstruction of the past, a quality of vividness deriving from their own immediacy, which can infuse the past with life. Obviously, it is the experience of transference affect that largely engages our attention in this reference. However, we must not ignore the contrapuntal role of the actual adult relationship between patient and analyst. Corresponding is indeed the actual biological constellation that bings the transference itself into being. At the very least, a minimal element of ‘resemblance’ to primary figures of the past is a sine quo non for its emergence (Stone 1954).
Nonetheless, this contribution up to and including Gill’s, Muslin’s (1976) and Gill’s (1979) are highly-developed. However, did not introduce alternations in the fundamental conceptions of psychopathology and its essential responses to analytic techniques and process. Yet, there are, of course, varying emphases - namely quantitative - and corresponding positions as to their respective effectiveness. As Strachey states, "there is an approach to actual substantive modification in the keystone position assigned to introjective super-ego change as the essential phenomenons of analytic process - and possibly in the exclusive role assigned to transference interpretations as ‘mutative’.
A related or complementary tendency may be discerned in Gill’s (1979) proposal that “analytic situation residues” from the patient’s ongoing personal life, insofar as they are judged transferentially significant in free association, is brought into relation with the transference as soon as possible, even if the patient feels no prior awareness of such a relationship. It is as if all significant emotional experience, including extra-analytic experiences, could be viewed as displacement or mechanisms of concealed expression of his transference. That this is very frequently true of even the most trivial-seeming actual allusions to the analytic would, in that, the thoroughly extra-analytic references constitute a more subtle and different problems, ranging from dubiously interpretably minor issues to massive forms of destructive acting out connected with extreme narcissistic resistances and utterly without discernible 'analytic situation residues'. The massive forms are, of course, analytic emergencies, requiring interpretation. Still, such interpretation would usually depend on the awareness of the larger ‘strategic situations (Stone 1973), rather than on a detail of the free association communication (granting the latter’s usefulness, if present - and recognizable). However, the fact of the past or the historical as never entirely abandoned or nullified, becoming more even, the role assigned to it may be pale or secondary. That the preponderant emphasis on concealed transference may ultimately, constitute an “actually existing” change in technique and process, with its own intrinsic momentum.
The Ferenczi and Rank technique included, in effect, a deliberate exploitation of the transference resistance, especially in the sense of intense emotional display and discharged. While the polemical emphases of these authors are on (affective) experiences as the sine non of true analytic process - the living through of what was never fully experienced in consciousness in the past (with ultimate translation into ‘memories’, i.e., constructions) - the actual techniques (with a few exceptions) are not clearly specified in their book. For a detailed exposition of the techniques learned from Ferenczi, with wholehearted acceptance, as in the paper of De Forest (1942), which includes the deliberate building up of dramatic transference intensities by interpretative withholding and the active participation of the analyst as a reactive individual. Also included is the active directing of all extra-therapeutic experience into the immediate experiential stream if the analysis. The extreme emphasis on affective transference experience became at one time a sort of vogue, appearing almost as an end and measured by the vehemence of the patient’s emotional displays. In Gill’s own revival of and emphasis on a sound precept of classical techniques (preceded by the 1976 paper of Gill and Muslin), fundamentally different from that of Ferenczi and Rank in its emphasis, one discerns an increment of enthusiasm between the studied, temperate, and well-argued paper of (1979) and the later paper of the same year (1979), which includes similar ideas greatly broadened and extended ti a degree that is, in it's difficultly to accept.
Now, what is it that may actually be worked out in the present - (1) as a prelude to genetic clarification and reduction of the transference neurosis or (2) as a theoretical possibility in its own right without reliance on the explanatory power or specific reductive impact of insight into the past? First some general considerations of whether or not one is an enthusiastic proponent of ‘object relations theory’ in any of its elaborate forms, seems self-evident that all major developmental vicissitudes and conflicts have occurred in the context of important relations with important objects and that they or their effects continue to be reflected in current relationships with persons of similar or parallel importance. That we assume that the psychoanalytic situation (and its adjacent ‘ extended family’) provides a setting in which such problems may be reproduced in their essentials, both effectively and cognitively.
There is something deductively engaging in the idea that an individual must confront and solve his basic conflicts in their immediate setting in which they arise, regardless of their historical background. Certainly this is true in the patient’s (or anyone else’s) actual life situation. Some possible and sometimes state corollaries of this view would be that the preponderant resort to the past, whether by recollection or reconstruction, would be largely in the service of resistance, in the sense of a devaluation of the present and a diversion from its ineluctable requirements. It would be as if the United Kingdom and Ireland would undertake to solve the current problems in Ulster essentially by detailed discussion of Cromwell’s behaviour a few centuries ago. Granted that the latter might indeed illuminate the historical contribution of some aspects of the current sociopolitical dilemma, there are immediate problems of great complexity and intensity from which the Cromwell discussion might indeed by a diversion, if it were magnified beyond it's clear but very limited contribution, displacing in importance the problematical social-political-economic altercation of the present and the recent clearly accessible and still relevant past. As with so many other issues, Freud himself was the first to note that resort to the past may be involved by the patient to evade pressing and immediate current problems. In conservative technique, it has long been noted that some judicious alternations of focus between past and present, according to the confronting resistances trend, may be necessary (for example, Fenichel 1945). However, it was Horney (1939) who placed the greatest stress on the conflict and the greatest emphasis on the recollection trend as supporting resistance.
Now, from the classical point of view, the emphasis is quite different. The original conflict situation is intrapsychic, within the patient, though obviously engaging his environment and ultimately - most poignantly and productively - his analyst. This culminates in a transference neurosis that reproduces the essential problems of the object relationships and conflicts of his development. Thus, in principle, the vicissitudes of love or hate or fear, etc., do not require, or even admit of, ultimate solution in the immediate reality, perceived and construed as such. The problem is to make the patient aware of the distortions that he has carried into the present and of the defensive modes and mechanisms that have supported them. Obviously, the process (‘tactical’) resistances present themselves first for understanding; later there are the ‘strategic’ resistances (i.e., those not expressed in manifest disturbances of free association) (Stoner 1973). Insofar as the mobilization of the transference and the transference neurosis is accorded a uniquely central holistic role in all analyses, the ‘resistance to the awareness of transference’, becomes a crucial issue, the problem of interpretive timing on which a controversial matter from early. Ultimately the bedrock resistance, the true ‘transference resistance’, must be confronted and dissolved or reduced to the greatest possible degree. Such a reduction is construed as largely dependent on the effective reinstatement of the psychological prototype of current transference illusions, with an ensuing sense of the inappropriateness of emotional attitudes in the present and the resultant tendency toward their relinquishment. In a sense, the neurosis is viewed as an anachronistic but compelling investitures of the current scene within unresolved conflict of the past. When successfully reduced, this does appear to have been the accessibly demonstrable phenomenology.
What then may be carried into the analytic situation from the ‘hard-nosed’ paradigm of the struggle with every day, current reality, with advantage to the process? We have already made mention, in that the sense of conviction, or ‘sense of reality’ - affective and cognitive - which originates in th immediacy of process experience. It is our purpose and expectation that, with appropriate skill and timing, this quality of conviction may become linked too other, fewer immediate phenomena, at least in the sense of more securely felt perceptions, including first the fact of transference and ultimately its accessible genetic origins. What furthers? Insofar as the transference neurosis tends toward organic wholeness, a sort of conflict ‘summary’ by condensation, under observation in the immediate present, one may seek and find access in it, not only to the basic conflict mentioned, but to uniquely personal mode of defence and resistance, revealed in dreams, habits of free association, symptomatic acts, parapraxes, and the more direct modes of personal address and interaction that are evident in every analysis. Further, in this view, although not always as transparent as one would wish, this remarkable condensation of effect, impulse, defence, and temporary conflict solution adumbrates more dependably than any other analytic element (or grouping of elements) the essential outlines of the field of obligatory analytic work of a given period of the patient’s life. In it is the tightly knotted tangle deprived from the patient’s early or prehistoric life enmeshed in him actualities of the analytic situation and his germane and contiguous ongoing life situations.
Also, in the sphere of the “here-and-now,” and of extensive importance, is the role of actualities in the analytic situation. Whether in the patent’s everyday life or in the analytic relationship, the even-handed, open-minded attention to the patient’s emotional experience (especially his suffering or resentment) as to what may be actual, as opposed too ‘neurotic’ (i.e., illusory or unwittingly provoked) or specifically transferential, is not only epistemologically deductive for reason that is also a contribution to the affective soundness of the basic analytic relationship and thus of inestimable importance. At the risk of slight - very slight - exaggeration, in that with excepting instances of pathological neurotic submissiveness, as a patient who wholeheartedly accepted the significance his neurotic or transference-motivated attitudes or behaviour if he felt that ‘his reality’ was not given just due. Furthermore, even the exploration and evaluation of complicated neurotic behaviour must be exhaustive to the point where a spontaneous urge to look for irrational motivations is practically on the threshold of the patient ‘s awareness. Once, again, one must stress the impact of such a tendency on the total analytic relationship. For, not only are the quality and mood of utilization of interpretations, but ultimately the subtleties of transition from a transference relationship to their realities of the actual relationship depend, on a greater degree than has been made explicit, on the cognitive and emotional aspects of the ongoing experience in the actual sphere. Greenson (1971, 1972. Wexler 1969) devoted several of his last papers to this important subject. The subject, of course, includes the vast spheres of the analyst’s character structure and his countertransference. However, more than may be at first apparency, can reside in the sphere of conscious consideration of technique e and attitude in relation to a basic rationale.
However, apart from the immediate function of painstaking discrimination of realities and the impact of this attitude on the total situation, there remains the important question of whether important elements of true analytic process may not be immanent in such trends of inquiry. The vigorous exploration and exposure of distortions in object relations, via the transference or in the affective and behavioural patterns of everyday life, including defence functions, can conceivably catalyse important spontaneous changes in their own right. To further this end, the traditional techniques of psychoanalysis will, of course, be utilized. As an interim phenomenon, however, the patient struggle to deal with distortions, as one might with other error subject to conscious control or pedagogical correction. It is to reasons of conviction that such a tendency may be productive (both as such, and in its intrinsic c capacity to highlight neurotic or conflictive fractions) and has been insufficiently exploited. Nonetheless, there is no reason that the specific dynamic impact of th past is lost or neglected in its ultimate importance, in giving attention to a territory that is, in itself, of a great technical potentiality.
Practitioners and theorists such as Horney (1939) or Sullivan (1953) did not reject the significance of the past, even though its role and proportionate position, both in process and theoretical psychodynamics, was viewed differently. The persisting common features in these views would be a large emphasis on sociological and cultural forces and the focussing of technical emphasis on immediate interpretation transactions.
Granted that various technical recommendations of both dissident and ‘classical’ origin, including those on the nature and reduction of the transference, sometimes appear to devaluate the operational importance of the genetic factor, this devaluation is not supported by the clinical experience of most of those that were indeed of closely scrutinizing it as part of the confessio fidei of major deviationists. Certainly, both in theoretical principle and in empirical observation, this essential direction of traditional analytic process remains of fundamental importance. Conceding the power and challenge of cumulative developmental and experiential personality change and the undeniable impact of current factors, it remains true that the uniquely personal, decisive elements in neurosis, apart from constitution, originate in early individual experience. How to mobilize elements into an effectively mutual function is largely a technical problem and - in seeming paradox - relies to a considerable degree on the skilful handling of the “here-and-now.” The purposive technical pursuit of the past has not been clinically rewarding. That the ultimate effort to recover an integrated early material in dynamic understanding may not always be successful, especially in severe cases of early pathogenesis is, of course, evident (for example, Jacobson 1971). In such instances, while our preference would be otherwise, we may have to remain largely content with painstaking work in the “here-and-now,” illuminated to whatever degree possible by reasonable and sound, if necessarily broad, constructions dealing largely with ego mechanisms than primitive anatomical fantasies. In other events, sometimes after years of painstaking work, even large and challenging characterological behavioural trends that have been viewed, clarified, and interpreted in a variety of current transference, situational (even cultural) references will show striking rottenness in earl y experience, conflict, and conflict solution whose explanatory value then achieves a mutative force that remains uniquely among interpretative manoeuvres or spontaneous insights. To this end, the broader aspects of ‘strategic’ resistance (Stone 1973) must be kept in mind, a much subtle element of countertransference and counterresistance.
It would seem proper that at this point of giving to a summation of the current ferment regarding the “here-and-now” of which any number of valuable critique and theoretical and technical suggestions that may help us to improve the analytic effectiveness, it would seem that the emphasis on the “here-and-now” interpreting not only consistently with but also ultimately indispensable for genuine access to the critical dynamism deriving from the individual’s early development. Nor is this reflexive, assuming the technical sophistication - inconsistent with the understanding and analysis of continuing developmental problems, character crystallization and the influence of current stresses as such. Adequate attention to the character as a complex interpretational group permits the clear and useful emergence in or the analytic field of significant early material, as defined by the transference neurosis between the technical approaches and that of Gill (1979, 1979), apart from certain larger issues. Whereas Gill would apparently recommend searching out ‘day residues’ of probable transference in the patient’s responses to the analysis or analyst and in his account of his daily life and offer possible alternative explanations to the patient’s direct and simple responses to them as self-evident realities, first relying on the acceptance and exploration of the patient’s ‘reality’, with the possibility that this will incidently favour the relatively spontaneous precipitation of more readily available transference materials, this general Principle does not, of course, obviate or exclude the other alternatives as something preferable?
Consideration of the interaction between the two adult personalties in the analytic situation requires a mixture of common sense and interest in self-evident (although often ignored) elements, on the one hand, and abstrusely psychological and Metapsychological considerations, on the other.
Thus, if we set aside from immediate consideration questions regarding the ‘real relationship’ and accept as a given self-evident fact that the entire psychoanalytic drama occurs (without our question or permission) between two adults in the “here-and-now” the residual is due becomes the management of the transference, which has been a challenging problem since the phenomenon was first described. Let us assume, for purposes of brevity, that few would now adhere to the principle that the transference is to be interpreted only when it becomes a manifest resistance (Freud 1912). It is in fact always a resistance and at the same time a propulsive force (Stone 1962, 1967, 1073). It has long since been recognized that an undue delay of well-founded transference interpretations (regardless of the state of the patient’s free association) can seriously hinder progress in analysis, and further, it cas augment the dangers of acting out or neurotic flight from the analysis by the patient. The awareness of such danger has been clearly etched in psychoanalytic consciousness since e Freud’s (1905) insight into the end of the Dora case.
Apart from the hazzards inherent in technical default, nonetheless, there has developed over the years with increasing momentum, perhaps in some relations of the increasing stress on the transference neurosis as a nuclear phenomenon of process. The affirmative active address to the transference, i.e., to the analysis - or some by time is the active interpretative bypassing - of the ‘resistances to the awareness of transference
. . . operational emphasis on the countertransference, the tendency - in rational for a proportion - must be regarded as an important integral component of a progressively evolving psychoanalytic method. That individuals vary in their acceptance of technical devotion to this tendency is to be note (as indicated earlier), but its widespread practice by thoughtful analysts cannot be ignored, by the importance of its disregarded note of countransference among analysts, which would tend to restore n earlier emphasis digestedly approach to historical material and avoidance of early or excessive; transference historical material and the avoidance of earlier excessive’ transference interpretation.
A few words about our view on th relatively a circumscribed problem of transference interpretation. It is of the belief of longstanding conviction that the economic aspects of transference distribution are critically important, although largely ignored the seeking utilization of this consideration, a broad directional sense, by distinguishing between the potential transference of the analytic situation and those of the typical psychotherapeutic situation (as beyond that, the transference of everyday life. These varying their degree of emergence and their special investment of transference objects with the intensiveness of contact, with the structural emends of deprivation, and with the degree of regressive attention the operation of the rule of abstinence, which is, of course, most highly developed and consistently maintained in the traditional psychoanalytic situation (Stone 1961). Thus although subject to constant infirmed monitoring, the transference can be as medical, at least latently directed ultimately toward the analyst (compared with the cooperated persons in their environment).
Now, under what conditions and with what provisions should the awareness of such transference potentialities be actively mobilized? Obviously, the original precept regarding its emergence as resistance still trued in its implied affirmative aspect but is no longer exclusive. Further, there are, without question, early transference ‘emergences’ that must be dealt with by an active interpretive approach: For example, the early rapid and severe transference regression of borderline patients or the less common some timely seriously impeding erotic transference fulminations in neuronic patients. These are special instances in which the indications seem clear and obligatory.
The central situation, nonetheless, is the ‘average’ analysis (with apologies!), where the latent transferences tend to remain ego-dystopia, warded off, deploring slowly over periods, and manifesting themselves by a variety of derivative phenomena of variable intensity. Surely, dreams, parapraxes, and trends of free association will reveal basic transference directions very early. However, when should these be interrelated to the patient if he is effectively unaware of them? Again, ‘all things' being equal’, an old principle of Freud’s suggested for all interpretative interventions (as opposed, for example, to clarification), is applicable: That unconscious elements are interpreted only when the patient evidences a secure positive attachment the analyst. Yet, this would not obtain in the fact of the ‘emergencies’ of growing erotic or aggressive intensities, certainly of ‘acting out’ is incipient. The disturbing compilations (even in the ‘erotic’ sphere) occur most often when basic transferences are ambivalent (largely hostile) or coloured by intense narcissism. Therefore, in relation to Freud’s valuable precept, it may be understood that in certain cases, the interpretation of ambivalent hostile transferences may be obligatory prerequisite to the establishment o f the genuinely positive climate that required. In such instances of obligatory intervention, the manifestations that require them are usually quite explicit,
Again, then, what about the relatively uncomplicated case, the chronic neurotic, potentially capable of relatively mature relations to objects? Still, the coping with complications do not seem as in question. There are, a few essential conditions and one cardinal rule. First the patient’s sense of reality and his common sense must not be abruptly or excessively tax, lest, in untoward reaction, his constructive imaginative capacities become unavailable. Preliminary explanations and tentative preparatory ‘trail’ interventions should be freely employed to accustom him to a new view of the world. The traditional optimum for interpretation (when the patient is on the verge of perceiving its content himself [Freud 1940] is indeed best, although it must sometimes be neglected in favour of an active interpretative approach. Second, the patient’s sense that the vicissitudes and exigencies of his actual situation are understood and respected must be maintained
Beyond these considerations, the essential principle is quite simple. If it is assumed that - in the intensive, abstinent, traditional psychoanalytic situation (as differentiated from most psychotherapeutic situations) - the transference (ultimately the transference neurosis) is ‘pointing’ toward the unconscious trend is heavily weighted in this direction, there is still a manifest element of movement toward other currently significant objects. Thus, a latent economic problem assumes clinical form: Essentially, the growing magnitude of transference cathexes of the analyst’s person, as withdrawn to varying degree from important persons in the environment with whom most of the patient’s associations usually deal. There is a point, or a phase, in the evolution of transference in which analytic material (often priori to significant subjective awareness) indicates the rapidly evolving shift from extraanalytic objects to the analyst. In this interval (early in some, later in others) the analyst’s interventions, whether in direct substantive form or aimed at resistances to awareness of transference, often become obligatory and certainly most often successful in mobilizing affective emphasis into the “here-and-now” of the analytic situation. The vigorous anticipatory interpretations suggested by some may be helpful in many instances (at least as preparatory manoeuvres) if (1) the analyst is certain of his views, in terms of not only the substance but the quantitative (i.e., economic) situation (2) the patient’s state soundly receptive (according to well-established criteria) (3) neither the patient’s realities nor his sense of their realities are put to unjustified questions or implicit neglect (4)a sense of proportion regarding the centrality of issues, largely as indicated by the outline of the transference neurosis (of their adumbration), are maintained in a real consideration. This will avoid the superfluous multiplication of transference references that like the massing of scatted genetic interpretations (familiar in the past), can lead to a ‘chaotic situation’ resembling that against which Wilhelm Reich (1933) inveighed. This will be more striking with a compliant patient who can as readily become bemused with his transference as with his ‘Oedipus’ or his ‘anality.’
Once the affective importance of the transference is established in the analysis, a further (hardly new) question arises, with which some of us have sought to deal in a therapist. Even if some agrees that transference interpretations have a uniquely mutative impact, how exclusively must we concentrate on them? Moreover, to what degree and when are extraanalytic occurrences and relationships of everyday life to be brought into the scope of transference interpretation? With regard to the concentration of transference interpretation alone: a large, complex, and richly informative worlds of psychological experience are obviously attention if the patient ‘s extra therapeutic life is ignored. Further, if the transference situation is unique in an affirmative sense, it is also unique by deficit. To revile at the analyst, for example, is a different experience from reviling at an employer who might ‘fire’ the patient or from being snide to a co-worker who might punch him (Stone 1067 and Rangell 1979). Such experiences are also components if the “here-and-now” (granted that the “here”aspect is significantly vitiated), and they do merit attention and understanding in their own right, specially in the sphere of characterology. Certain complex reaction pasterns cannot become accessible in the transference context alone.
At the time of speaking it is true that many spectacular extraanalytic behaviours can, and should be seen as displacements (or ‘acting out’) of the analytic transference or in juxtaposed ‘extended family’ relation to it, especially where they involve consistent members of an intimate dramatis personae? While such ‘extra-therapeutic’ transference interpretations (often clearly Germaine to the conflicts of the transference neurosis) can be indispensable, the confronting vigour and definiteness with which they are advanced (as opposed to tentativeness) must always depend on the security of knowledge of preceding and current unconscious elements that invest the persons involved.
Finally, there are incidents, attitudes, and relationships to persons in the patient’s life experience who are not demonstrably involved in the transference neurosis, yet evoke importantly and characteristic responses whose clarification and interpretation may contribute importantly to the patient’s self-knowledge of defences, character structure, and allied matters. Nonetheless, such data may occasionally show a vitalizing direct relationship to historical materials. It would not seem necessary or desirable that such material be forced into the analytic transference if the patient does not respond to a tactful tentative trail in this connection, for example, the ‘alternative’ suggestion proposed by Gill (1979). For the economic considerations that often obtain, and it may be that certain concurrent transference cluster, not readily related to the mainstream of transference neurosis, retain their own original extra-therapeutic transference investment. In some instances, a closer, more available e relationship to the transference mainstream may appear later and lend itself to such interpretative integration. In so doing, happening is likely if obstinate resistances have not been simulated by unnecessary assault on the patients' sense of immediate reality, or his sense of his actual problems. As for metapsychology, one may recall also that all relationships, following varying degrees of development and conflict vicissitudes, are derived greatly from the original relationship to the primal object (Stone 1967), even if their representations are relatively free of the unique ‘unneutralized’ cathexes that characterize active transference (‘transfer’ verus ‘transference’: Stern 1957).
Caring for a better understanding, to what the concerning change, as seen in the psychotherapy of schizophrenic patient, and particularly in reference to the sense of personal identity, may to this place be clearly vitiated in material that relates to extra-therapeutic experience, whether this is seen ‘in its own right’ or as displaced transference. The direct transference experience occurs in relations an individual who knows his own position, i.e., knows ‘both sides’ as in no other situation. (Even where there are interposing countertransference. There are at least susceptible to a self-analysis). This can never be true in the analysis of an extra-therapeutic situation, as there is no inevitable cognitive deficit. For this we must try to compensate by exercising maximal judgement, by exploiting what is revealed about the patient himself in sometimes unique situations, and by being sensitive to the growing accuracy of his reporting as the analyst progresses. Epistemologic deficits' are intrinsic in the very nature of analytic work. This is but one important example.
We need to be alert to the respects in which the concepts and technique of our particular science may lend themselves to the repression, in us and our patients, of anxiety concerning change.
Our necessary delineation of the repetitive patterns between the transference and countertransference tends to become so preoccupying as to obscure the circumstance that, as Janet M. Rioch phrases it, “What is curative in the [analytic] process is that in tending to reconstruct in which the analyst that an atmospheric state that obtained in childhood, the patient effectively achieves something new” (Rioch 1943).
Our necessarily high degree of reliance upon verbal communication requires us to be aware of the extent to which grammatical patterns having a tendency to segment and otherwise render static our ever-flowing experience; this has been pointed out by Benjamin (1944); Bertrand Russell (1900), Whorf (1956) and others. The tendency among us to regard prolonged silence for being given to disruptiveness in the analytic process, or evidence per se of the patient’s resistance to it, may be due in part to our unconscious realization that profound personalty-change is often best simplified by silent interaction with the patient; therefore, we have an inclination to press forward toward the crystallization of change-inhibiting words.
What is more, our topographical views of the personality a being divisible into the area’s id, ego, and superego, are so inclined to shield us from the anxiety-fostering realization that, in a psychoanalytic cure, change is not merely quantitative and partial
as of “Where id was, there shall Ego be,” in Freud’s dictum, but qualitative and all-pervasive. Apparently such data system in a passage is to provide accompaniment for Freud, as he gives a picture of personality-structure, and of maturation, which leaves the inaccurate but comforting impression that at least a part of us - namely, a part of the id - is free from change. In his paper entitled Thought for the Times on War and Death. In 1915, he said, "the evolution of the mind shows a peculiarity that is present in no other process of development." When a village grows into a town, a child into a man, the village, and the child become submerged in the town and the man. . . . It is in other considerable levels that the accompaniment with the development of the mind . . . the primitive stage [of mental development] can always be re-established; the primitive mind is, in the fullest meaning of the word, imperishable (Freud 1915).
In Introductory Lectures on Psycho-Analysis, he says that “in psychoanalytic treatment. . . . By means of the work of interpretation, which transform what is unconscious into what is conscious, the ego is enlarged at the expense of this unconscious.” In the Ego and the Id, he said that, " . . . the ego is that part of the id modified by the direct influence of the external world . . . the pleasure-principle . . . reigns unrestricted by the id. . . . The ego represents what may be called reason and common sense, in contrast to the id, which contains the passions” (Freud 1923).
Glover, in his book on Technique published in 1955, states similarly that, . . .” A successful analysis may have uncovered a good deal of the repressed . . . [and] have mitigated the archaic censoring functions of the superego, but it can scarcely be expected to abolish the id” (Glover 1955).
Favorably to have done something to provide by some measure, conviction, feeling, mind, persuasion, sentiment used to form or be expressed of some modesty about the state of development of our science, and about our own individual therapeutic skills, should not cause us to undertake the all-embracing extent of human personality growth in normal maturation and in a successful psychoanalysis. Presumably we have all encountered a few fortunate instances that have made us wonder whether maturation really leaves any area of the untouched personality, leaves any steel-bound core within which the pleasure principle reigns immutably, or whether, instead, we have a genuine metamorphosis, from a former hateful and self-seeking orientation to a loving and giving orientation, quite as wonderful and thoroughgoing as the metamorphosis of the tadpole into the frog or that of the caterpillar into the butterfly.
Freud himself, in his emphasis upon the ‘negative therapeutic reaction’ (1923), the repetition compulsion, and the resistance to analytic insight that he discovered in his work with neurotic patients, has shown the importance, in the neurotic individual, of anxiety concerning change, and he agrees with Jung’s statement that ‘a peculiar psychic inertia, hostile to change and progress, is the fundamental condition of neurosis’ (Freud 1915). This is, even more true of the psychosis - so much so that only in very recent decades have psychotic patients achieved full recovery through modified psychoanalytic therapy. Also, it has instructively to explore and deal the psychodynamics of schizophrenia as for the anxiety concerning change which one encounters, in a particular intense degree, at work in these patients, and of ones own, inasmuch as for treating them. What the therapy of schizophrenia can teach us of the human being’s anxiety concerning change, can broaden and deepen our understanding of the non-psychotic individual also.
Further, we see that during his development years he lacks adequate models, in his parents or other parent-figures, with whom to identify about the acceptance of outer changes and the integration of inner change as personality-maturation throughout adulthood. Alternatively, these are relatively rigid persons who, over the years, either/or tenaciously resist change, if anything becomes progressively constricted, fostering him in the conviction that the change from a child into adult is more loss than gain - that, as one matures, fewer feelings and thoughts are acceptable, until finally one is to attain, or be confined to, the thoroughgoing sterility of adulthood. The sudden, unpredictable changes that puncture his parent’s rigidity, due to the eruption of masses of customarily-repressed material in themselves, make them appear to him, for the time being, like totally different persons from their usual selves, and this adds to his experience that personality-change is something that is not to be striving for, but avoided as frighteningly destructive and overwhelming.
We find evidence that he is reacting to, by his parents during his upbringing, predominantly concerning transference and projection, for being the reincarnation of some figure or figures from their own childhood, and the personification of repressed and projected personality-traits in themselves. Thus he is called upon by them, in an often unpredictably changing fashion, to fill various rigid roles in the family, leaving him little opportunity to experience change as something that can occur within himself, as a unique human individual, in a manner beneficial to himself.
When the parents are not relating to him in such a transference fashion they are, it appears, all too often narcissistically absorbed in them. In either instance, the child is left largely in a psychological vacuum, in that he has to cope essentially alone with his own maturing individuality, including the intensely negative emotions produced by the struggle for individuality in such a setting. Because his parents are afraid of the developing individual in him, he too fears this inner self, and his fear of what is heightening parenthetical parents within investing him with powers, based upon the mechanisms of transference and projection that by it's very nature does not understand, powers that he experiences as somehow flowing from himself and yet not an integral part of himself nor within his power to control. As the years bring tragedies to his family, he develops the conviction that he somehow possesses all ill-understood malevolence that is totally responsible for these destructive changes.
In as far as he does discover healthy maturational changes at work in his body and personality, changes that he realizes to be wonderful and priceless, he experiences the poignant accompanying realization that there is no one there to welcome these changes and to share his joy. The parents, if sufficiently free from anxiety to recognize such changes at all, have a tendency to accept them as evidence that their child is rejecting then by growing functionally. Also to be noted, in this connexion, is their lack of trust in him, their lack of assurance that he is elementally good and can be trusted to maturational bases of a good healthy adult. Instead they are alert to find, and warn him against, manifestations in him that can be construed as evidence that he is on a predestined, downward path into an adulthood of criminality, insanity, more at best ineptitude for living.
Moreover, he emergences change not as something within his own power to wield, for the benefit of himself and others but as something imposed from without. This is due not only to structures that the parents place upon his autonomy, but also to the process of increasing repression of his emotions and life as, such that when this latter manifest themselves, they do so in a projected expressive style, for being uncontrollable changed, inflicted upon him from the surrounding world? We see extreme examples of this mechanism later on. In the full-blown schizophrenic person who experiences sexual feelings not as such but as electric shocks sent into him from the outside world, and who experiences anger not as an emerging emotion directorially fittingly as in a way up from within, but a massive and sudden blow coming somehow from the outer world. In fewer extreme instances, in the life of the yet-to-become-schizophrenic youth, he finds repeatedly that when he reaches out to another person, the other suddenly undergoes a change in demeanour, from friendliness to antagonism, in reaction to an unwitting manifestation of the youths’ unconscious hostility. The youth himself, if unable to recognize his own hostility, can only be left feeling increased helplessness in face of an unpredictably changeable world of people.
The final incident that occurs before his admission to the hospital, giving him still further reason for anxiety as for change, is his experience of the psychotic symptoms as an overwhelming anxiety-laden and mysterious change. His own anxiety about this frightened away by the seismic disturbance and horror of the members of his family who finds hi ‘changed’ by what they see as an unmitigated catastrophe, a nervous or mental ‘breakdown’. Although the therapist can come to see, in retrospect, a potential positive element via this occurrence - namely, the emergence of onetime-repressed insights concerning the true state of affairs involving the patient and his family, none of those participants can integrate so radically changed a picture at that time. Over the preceding years the family members could not tolerate their child’s seeing himself and them with the eyes of a normally maturing offspring, and when repressed percepts emerge from repression in him, neither they nor he possesses the requisite ego-strength to accept them as badly needed changes in his picture of himself and of them. Instead, the tumult of depressed percepts foes into the formation of such psychotic phenomena as misidentifications, hallucinations, and delusions in which neither he nor the member of his family can discern the links to reality that we, upon investigation in individual psychotherapy with him, can find in these psychotic phenomena - links, that is, to the state of affairs that has really held sway in the family. Paretically, it should be marked and noted that the psychotic episode often occurs in such ac way as to leave the patient especially fearful of sudden change, for in many instances the de-repressed material emerges suddenly and leads him to damage, in the short space of a few hours or even moments, his life situation so grievously that repair can be affected only very slowly and painfully, over many subsequent months of treatment in the confines of a hospital.
It should be conveyed, in that the regression of the thought-processes, which occurs as one of the features of the developing schizophrenia, results in an experience of the world so kaleidoscopic as to make up still another reason for the individual’s anxiety concerning change. That is, as much as he has lost thee capacity to grasp the essentials of a given whole - to the extent that he has regressed to what Goldstein (1946) terms the ‘concrete attitude’ - he experiences any change, even if it is only in an insignificant (by mature standards) detail of that which he perceives, as a metamorphosis that leaves him with no sense of continuity between the present perception and that immediately preceding. This thought disorder, various aspects of which have been described also by Angyal (1946), Kasanin (1946), Zucker (1958), and others, is compared by Werner with the modes of thought that are found in members of so-called primitive cultures (and in healthy children of our own culture): . . . in the primitive mentality, particulars often as self-subsisting things that do not necessarily become synthized into larger entities. . . . The natives of the Kilimanjaro region do not have a word for the whole mountain range that they inhabit, only words for its peaks. . . . The same is reported of the aborigines of East Australia. From each twist and turn of a river has a name, but the language does not permit of a single all-embracing differentiation for the whole river. . . . [He] quotes Radin (1927) as saying that for the primitive man: “A mountain is not thought of as a unified whole. It is a continually changing entity’ . . . [and, Radin continues, such a man lives in a world that is] ‘dynamic and ever-changing . . . Since he sees the same objects changing in their appearance from day to day, the primitive man regards this phenomenon as definitely depriving them of immutability and self-subsistence’ (Werner 1957).
Langer (1942) has called the symbolic-making function ‘one of man’s primary activities, like eating, looking, or moving about. It is the fundamental process of his mind’, she says, as she terms the need of symbolization ‘a primary need in man, which other creatures probably do not have’. Kubie (1953) terms the symbolizing capacity ‘the unique hallmark of man . . . capacities’, and he states that it is in impairment of this capacity to symbolize that all adult psychopathology essentially consists.
As for schizophrenia, we find that since 1911 this disease was described by Bleuler (1911) as involving an impairment of the thinking capacities, and in the thirty years many psychologists and psychiatrists, including Vigotsky (1934) Hanfmann and Kasanin (1942) Goldstein (1946) Norman Cameron (1946) Benjamin (1946) Beck (1946) von Domarus (1946) and Angtal (1946) - to mention but a few - has described various aspects of this thinking disorder. These writers, agreeing that one aspect of the disorder consists in over -concreteness or literalness of thought, have variously described the schizophrenic as unable to think in figurative (including metaphorical) terms, or in abstractions, or in consensually validated concepts and symbols, mor in categorical generalizations. Bateson (1956) described the schizophrenic as using metaphor, but unlabelled metaphor.
Werner (1940) has understood this most accurately matter of regression to a primitive level of thinking, comparable with the found in children and in members of so-called primitive cultures, a level of thinking in which there is a lack of differentiation between the concrete and the metaphorical. Thus we might say that just as the schizophrenic is unable to think in effective, consensually validated metaphor, as too as he is unable to think in terms that are genuinely concrete, free from an animistic forbear of a so-called metaphorical overlay.
The defensive function of the dedifferentiation that in so characterized of schizophrenic experience, and one find that this fragmentation o experience, justly lends itself to the repression of various motions that are too intense, and in particular too complex, for the weak ego to endure, which must be faced as one becomes aware of change as involving continuity rather than total discontinuity.
That is, the deeply schizophrenic patient who, when her beloved therapist makes a unkind or stupid remark, experiences him now for being a different person from the one who was there a moment ago - who experiences that a Bad Therapist has replaced the Good Therapist - is by that spared the complex feeling of disillusionment and hurt, the complex mixture of love and anger and contempt that a healthier patient would feel then. Similarly, if she experiences it in tomorrow’s session - or even later in the same session - that another good therapist has now come on the scene. The bad therapist is now totally gone, she will feel none of the guilt and self-reproach that a healthier patient would feel at finding that this therapist, whom she has just now been hated or despising, is after all a person capable of genuine kindness. Likewise, when she experiences a therapist’s departure on vacation for being a total deletion of him from her awareness, this bit of discontinuity, or fragmentation, in her subjective experience spars her from feeling the complex mixture of longing, grief, separation-anxiety, rejection, rage and so on, which a less ill patient feels toward a therapist who is absent but of whose existence he continues to be only too keenly aware.
Finally, such repressed emotions as hostility and lust may readily be seen, as these feelings not easy to hear expressed, as, for instance, the woman, who, at the beginning of her therapy, had been encased for years I flint lock paranoid defenses, become able to express her despair by saying that “If I had something to get well for, it would make a difference,” her grief, by saying, “The reason I am afraid to be close to people is because I feel so much like crying”: Her loneliness, by expressing a wish that she would turn an insect into a person, so then she would have a friend. Her helplessness in face of her ambivalence by saying, to her efforts to communicate with other persons, “I feel just like a little child, at the edge of the Atlantic or Pacific Ocean, trying to build a castle - right next to the water. Something just starts to be gasped [by the other person], and then bang! It has gone - another wave. As joining the mainstream of fellow human beings.
In the compliant charge of bringing forward three hypotheses are to be shown, they're errelated or portray in words as their interconnectivity, are as (1) in the course of a successful psychoanalysis, the analyst goes through a phase of reacting to, and eventually relinquishing, the patient as his oedipal love-object, (2) in normal personality development, the parent reciprocates the child's oedipal love with greater intensity than we have recognized before, and (3) in such normal developments, the passing of the Oedipus complex is at least important a phase in ego-development as in superego-development.
While doing psycho-analysis, time and again patients who have progressed to, or very far toward, a thorough going analysis to cure, become aware of experiential romantic and erotic desires and fantasies. Such fantasizing and emotions have appeared in a usual but of late in the course of treatment, have been preset not briefly but usually for several months, and have subsided only after having experienced a variety of feelings - frustration, separation anxiety, grief and so forth - entirely akin to those that attended as the resolution of an Oedipus complex late in the personal analysis.
Psycho-analysis literature is, in the main. Such as to make one feel more, rather than less, troubled at finding in oneself such feelings toward one's patient. As Lucia Tower (1956) has recently noted, . . . Virtually every writer on the subject of countertransference . . . states unequivocally that no form of erotic reaction to a patient is to be tolerated . . .
Still, in recent years, many writers, such as P. Heimann (1950), M. B. Cohen (1952) and E. Weigert (1952, 1954), have emphasized how much the analyst can learn about the patient from noticing his own feelings, of whatever sort, in the analytic relationship. Weigert (1952), defining countertransference as emphatic identification with the analysand, has stated that . . . "In terminal phases of analyses the resolution of countertransference goes hand in hand with the resolution of transference."
Respectfully, these additional passages are shown in view of countertransference, in the special sense in which defines the analyst for being innate, inevitable ingredients in the psycho-analytic relationship, in particular, the feelings of loss that the analyst experiences with the termination of the analysis. However, case in point, that the particular variety of countertransference with which are under approach is concerned that of the analyst's reacting as a loving and protective parent to the analysand, reacted too as an infant: There are plausible reasons why in the last phase it is especially difficult to achieve and maintain analytic frankness. The end of analysis is an experience of loss that mobilizes all the resistances in the transference (and in the counter-transference too), for a final struggle. . . . Recently, Adelaide Johnson (1951) described the terminal conflict of analysis as fully reliving the Oedipus conflict in which the quest for the genitally gratifying parent is poignantly expressed and the intense grief, anxiety and wrath of its definitive loss are fully reactivated. . . . Unless the patient dares to be exposed to such an ultimate frustration he may cling to the tacit permission that his relation to the analyst will remain his refuge from the hardships of his libidinal cravings to an aim-inhibited, tender attachment to the analyst as an idealized parent, he can get past the conflicts of genital temptation and frustration.
. . . . The resolution of the counter-transference permits the analyst to be emotionally freer and spontaneous with the patient, and this is an additional indication of the approaching end of an analysis.
. . . . When the analyst observes that he can be unrestrained with the patient, when he no longer weighs his words to maintain as cautious objectivity, this empathic countertransference and the transference of the patient are in a process of resolution. The analyst can treat the analysand on terms of equality; he is no longer needed as an auxiliary superego, an unrealistic deity in the clouds of detached neutrality. These are signs that the patient's labour of mourning for infantile attachments nears completion.
In stressing the point, which before an analysis can properly bring to an end, the analyst must have experienced a resolution of his countertransference to the patient for being a deep beloved, and desired, figure not only on this infantile level that Weigert has emphasized valuably, but also on an oedipal-genital level. Weigeret's paper, which helped to formulate the views that are set down, that is, as expressing the total point that a successful psycho-analysis involves the analyst's deeply felt relinquishment of the patient both as a cherished infant, and for being a fellow adult who is responded to at the level of genital love?
The paper by L. E. Tower (1956) comes similarly close to the view that, unlike Weigert, limits the term counter-transference to those phenomena that are transferences of the analyst to the patient. It is much more striking, therefore, that she finds even this classification defined countertransference to be innate to the analytic process: . . . . That there is inevitably, naturally, and often desirable, many countertransference developments in every analysis (some evanescent - some sustained), which is a counterpart of the transference phenomena. Interactions (or transactions) between the transference of the patient and the countertransference of the analyst, going on at unconscious levels, may be - or perhaps are always - of vital significance for the outcome of the treatment. . . .
. . . . Virtually every writer on the subject of countertransference. States unequivocally that no form of erotic reaction to a patient is to be tolerated. This would suggest that temptations in this area are great, and perhaps ubiquitous. This is the one subject about which almost every author is very certain to state his position. Other 'counter-transference' manifestations are not routinely condemned. Therefore, it must be to assume that erotic responses to some extent trouble nearly every analyst. This is an interesting phenomenon and one that call for investigation; nearly all physicians, when they gain enough confidence in their analysts, report erotic feelings and imply toward their patients, but usually do so with a good deal of fear and conflict. . . .
Of our tending purposes, we are to pay close attention to the libidinal resources that are of our applicative theory, in that large amounts of resulting available libido are necessary to tolerate the heavy task of many intensive analyses. While, we deride almost every detectable libidinal investment made by an analyst in a patient . . . various forms of erotic fantasy and erotic countertransference phenomena of a fantasy and of an affective character are in some experiential ubiquitous and presumably normal. Which lead to suspect that in many - perhaps every - intensive analytic treatment there develops something like countertransference structures (perhaps even a 'neurosis') which are essential and inevitable counterparts of the transference neurosis. These countertransference structures may be large or small in their quantitative aspects, but in the total picture they may be of considerable significance for the outcome of the treatment. They function in the manner of a catalytic agent in the treatment process. Their understanding by the analyst may be as important to the final working through of the transference neurosis as is the analyst's intellectual understanding of the transference neurosis itself, perhaps because they are, so to speak, the vehicle for the analyst's emotional understanding of the transference neurosis. Both transference neurosis and countertransference structure seem intimately bound together in a living process and both must be considered continually in the work that is the psychoanalysis. . . .
. . . . Seemingly questionable, is any thorough working through a deep transference neurosis, in the strictest sense, which does not involve some form of emotional upheaval in which both patient and analysts are involved. In other words, there are both a transference neurosis and a corresponding Countertransference 'neurosis' (no matter how small and temporary) which are both analyzed in the treatment situation, with eventual feelings of a new orientation by both one another toward any other but themselves.
Freud, in his description of the Oedipus complex (1900, 1921, 1923), tended largely to give us a picture of the child as having an innate, self-determined tendency to experience, under the conditions of a normal home, feelings of passionate love toward the parent of the opposite sex; we get little hints, from his writings, that in this regard the child enters a mutual relatedness of passionate love with that parent, a relatedness in which the parent's feelings may be of much the same quality and intensity as those in the child (although this relatedness must be very important in the life of the developing child than it is in the life of the mature adult, with his much stronger, more highly differentiated ego and with his having behind him the experience of a successfully resolved oedipal experience during his own maturation).
Nevertheless, in the earliest of his publications concerning the Oedipus complex, namely The Interpretation of Dreams (1900), Freud makes a fuller acknowledgements of the parent's participation in the oedipal phase of the child's life than does in any of his later writings on the subject". . . a child's sexual wishes - if in their embryonic stage they deserve to be so described - awaken very early. . . . A girl's first affection is for her father and boy's first childish desires are for his mother. Accordingly, the father becomes a disturbing rival to the boy and the mother to the girl. The parents too give evidence as a rule of sexual partiality: A natural predilection usually sees to it that a man tends to spoil his little daughters, while his wife takes her sons' part; though both of them, where their judgement is not disturbed by the magic of sex, keep a strict eye upon their children's education. The child is very well aware of this patriality and turns against that one of his parents who is opposed to showing it. Being loved by an adult does not merely bring a child the satisfaction of a special need; it also means that he will get what he wants in every other respect as well. Thus, he will be following his own sexual instinct and while giving fresh strength to the inclination shown by his parents if his choice between them falls in with theirs (1900).
Theodor Reik, in his accounts of his coming to sense something of the depths of possessiveness, jealousy, fury at rivals, and anxiety in the face of impending loss, in himself regarding his two daughters, conveys a much more adequate picture of the emotions that genuinely grip the parent in the oedipal relationship than is conveyed by Freud's sketchy account, as Reik's deeply moving descriptions occupy a chapter in his Listening with the Third Ear (1949), written at the time when his daughters were twelve and six years of age; and a chapter in his The Secret Self (1952), when the oldest daughter was now seventeen.
Returning to a further consideration of the therapist's oedipal-love responses to the patient, it seems that these response flows from four different sources. In actual practice the responses from these four tributaries are probably so commingled in the therapists that it is difficult of impossible fully to distinguish one kind from another; the important thing is that he is maximally open to the recognition of these feelings in himself, no matter what their origin, for he can probably discern, in as far as is possible, from where they flow they signify, therefore, concerning the patient's analysis.
First among these four sources may be mentioned the analyst's feeling-responses to the patient's transference. This, when, as the analysis progresses and the patient enter an experiencing of oedipal love, ongoing, jealousy y, frustration and loss as for the analyst as a parent in the transference, the analyst will experience to at least some degree, response's reciprocally th those of the patient-responses, that is, such for being present within the parent in questions, during the patient's childhood and adolescence, which the parent presumably was not ably to recognize freely and accept within himself. Some writers apply the term 'counter-transference' to such analyst-responese to the patient's transference, unlike others some do not do so.
The second source consists in the countertransference in the classical sense in which this term is most often used: The analyst's responding to the patient about transference-feelings carried over from a figure out of the analyst 's own earlier years, without awareness that his response springs predominantly from this early-life, rather than being based mainly upon the reality of the patient analyst-patient relationship. It is this source, of course, which we wish to reduce to a minimum, by means of thoroughgoing personal analysis and ever-continuing subsequent alertness for indications that our work with a patient has come up against, in us, unanalyzed emotional residues from our past. This source is so very important, in fact, as to make the writing of such a paper as a somewhat precarious venture. Must expect that some readers will charge him with trying to portray, as natural and necessary to the annalistic process generally, certain analyst-responese that in actuality is purely the result of an unworked-through? Oedipus' complex in himself, which are dangerously out of place in his own work with patients that have no place in the well-analysed analyst's experience with his patient.
It can only be surmised that although this source may play an insignificant role in the responses of a well-analysed analyst who has conducted many analyses through to completion - to an intensified inclusion as a thoroughgoing resolution of the patient's Oedipus complex - it is probably to be found, in some measure, in every analyst. This is, it seems that the nature and conflictual feeling-experience in this regard - a fostering of his deepest love toward the fellow human being with whom she participates in such prolonged and deeply personal work, and a simultaneous, unceasing, and rigorous taboo against his behavioural expression of any of the romantic or erotic components of his love - as to require almost any analyst's tending to relegate the deepest intensities of these conflictual feelings to his own unconscious mind, much as were the deepest intensities of his oedipal strivings toward a similar beloved, and similarly unobtainable and rigorously tabooed, parent in particular, and in the hope of the remaining in the analyst's unconscious. That is hoping that this will help analysts - in particular, to a lesser extent-experienced analyst - whereas to some readers awareness, and by that diminution, of this countertransference feeling, as justly dealing with other kinds of countertransference feelings, by such as those wrote by P. Heumann (1950, M. B., Cohen (19520 and E. Weigert (1952?)
A third source is to be found in the appeal that the gratifyingly improving patient makes to the narcissistic residue in the analyst's personality, the Pygmalion in him. He tends to fall in love with this beautifully developing patient, regarded at this narcissistic level as his own creation, just as Pygmalion fell in love with the beautiful statu e of Galatea that he had sculptured. This source, like the second one that we can expect to holds little sways in the well-analysed practitioner of long experience, but it, too, is probably never absent of great experience and professional standing, than we may like to think. Particularly in articles and books that describe the author's new technique or theoretical concept as an outgrowth of the work with a particular patient, or a very few patients, do we see this source very prominently present in many instances.
The fourth source, based on the genuine reality of the analyst-patient situation, consists in the circumstance that nearly becomes, per se, a likeable, admirable and insightfully speaking lovable, human being from whom the analyst will soon become separated. If he is not himself a psychiatrist, the analyst may very likely never see him again. Even if he is a professional colleague, the relationship with him will become in many respects far more superficial, far less intimate, than it has been. This real and unavoidable circumstance of the closing analytic work tends powerfully to arouse within the analyst feelings of painfully frustrated love that deserve to be compared with the feelings of ungratifiable love that both child and parent experience in the oedipal phase of the child's development. Feelings from this source cannot properly be called countertransference. They may flow from the reality of the present circumstances but they may be difficult or impossible e to distinguish fully from countertransference.
There are, then four essentially powerful sources having to promote of the tendency toward the feelings of deep love with romantic and erotic overtones, and with accompanying feelings of jealousy, anxiety, frustration-rage, separation-anxiety, and grief, in the analyst about the patient. These feelings come to him, like all feelings, without tags showing from where they have come, and only if he is open and accepting to their emergence into his awareness does he have a chance to set about finding out their origin and thus their significance in his work with the patient.
Finally, with which the considerations have been presented so far, a few remarks concerning the passing of the Oedipus complex in normal development and in a successful psycho-analysis.
In the Ego and the Id (1923) we find italicized a passage in which Freud stresses that the oedipus phase results in the formation of the superego; we find that he stresses the patient's opposition to ther child's oedipal swosh, and lastly, we see this resultant suprerego to be predominantly a severe and forbidding one: The broad general outcome of the sexual phase dominated by the Oedipus complex may, therefore, be taken to be the forming of a precipitating in the ego . . . This modification of the ego
. . . comforts the other contents of the ego as an ego ideal or super-ego.
. . . . The child's parents, and especially his father, were perceived as the obstacle to verbalizations of his Oedipus wishes, so his infantile ego fortified itself for the carrying out of the repression by building this obstacle within itself. It borrowed the strength to do this, so to seek, from the father, and this loan was an extraordinarily nonentous act. The super-ego retains the character of the father, while the more powerful the Oedipus complex was and the more rapid succumbed to repression (under the influence of authority, religious teachings, schooling and reading), this strictly will be the domination of the super-ego over the ego later on - as conscience or perhaps of an unconscious sense of guilt. . . .
The subject dealt within the subjective matter through which generative pre-oedipal origins are to be found of the superego, on which has been dealt by M. Klein (1955). E. Jacobson (1954) and others, also apart from that subject, a regard for Freud's above-quoted description as more applicable to the child who later becomes neurotic or psychotic, than to the 'normal'; child. Since we can assume that there is virtually a wholly complimentary neurotic difficulty, we may then have in assuming that Freud's formation holds true to some degree in every instance. Still, to the extent that a child's relationships with his parents are healthy, he finds the strength to accept the unrealizibilityy of his oedipal strivings, not mainly through the identification with the forbidding rival-parent, but mainly, as an alternative, the ego-strengthening experiences of finding the beloved parent reciprocate his love - responds to him, that is, for being a worthwhile and loveable individual, for being, a conceivably desirable love-partner - and renounces him only with an accompanying sense of loss on the parent's own part. The renunciation, again, something that is mutual experience for the chid and parent, and is made in deference to a recognizedly greater limiting realty, a reality that includes not only the taboo maintained by the rival-parent, but also the love of the oedipal desired parent toward his or her spouse - a love that undeterred the child's birth and a love to which, in a sense, he owes his very existence?
Out of such an oedipal situation the child emerges, with no matter how deep and painful sense of loss at the recognition that he can never displace the rival-parent and posses the beloved on e in a romantic-and-erotic relationship, in a state differently from the ego-diminished, superego-domination state that Freud described. This child that his love, however unrealized, is reciprocated. Strengthened, too, out of the realization, which his relationship with the beloved parent has helped him to achieve, that he lives in a wold in which any individual's strivings are encompassed by a reality much larger than he: Freud, when he stressed that the oedipal phase normally results mainly in the formations of a forbidding superego, and if it is resulting mainly in enchantments of the ego's ability to test both inner and outer reality.
All experiences with both neurotic and psychotic patients had shown that, in every individual instance, in as far as the oedipal phase was entered the course of their past elements, it led to ego impairment rather than ego functioning as primarily because the beloved parent had to repress his or her reciprocal desire for the child, chiefly through the mechanism of unconscious denial of the child's importance to the parent. More often than not, in these instancies, that suggested that the parent would unwittingly act out his or her repressed desires in the unduly seductive behaviour toward the child; yet whenever the parents come close to the recognition of such desires within him, he would unpredictably start reacting to the child as unlovable - undesirable.
With many of these parents, appears that, primarily because of the parent's own unresolved Oedipus complex, his marriage proved too unsatisfying, and his emotional relationship to his own culture too tenuous, for him to dare to recognize the strength of his reciprocal feelings toward his child during the latter's oedipal phase of development. The child is reacting too as a little mother or father transference-figure to the parent, a transference-figure toward whom the parent's repressed oedipal love feelings are directed. If the parent had achieved the inner reassurance of a deep and enduring love toward his wife, and a deeply felt relatedness with his culture including the incest taboos to which his culture adheres, he would have been able to participate in as deeply felt, but minimally acted out, relationship with the chid in a way that fostered the healthy resolutions of the child's Oedipus complex. Instead, what usually happens in such instances, in that the child's Oedipus complex remains unresolved because the child stubbornly - and naturally - refuses to accept defeat within these particular family circumstances, whereas the acceptance of oedipal defeat is tantamount to the acceptance of irrevocable personal worthlessness and unlovability.
It seems much clearer, then this former child, now neurotic or psychotic adult, requires from us for the successful resolution to his unresolved Oedipus complex: Not such a repression of desire, acted-out seductiveness, and denial of his own worth as he met in the relationship with his parent, but a maximal awareness on our part of the reciprocal feelings while we develop in response to his oedipal strivings. Our main job remains always, of course, to further the analysis of his transference, but what might be described seems to be the optimal feeling background in the analyst for such analytic work.
Formidably, when applied not to a moderate degree found in the background of the neurotic person but invested with all the weight of actual biological attributes, have much ado with the person's unconscious refusal to relinquish, in adolescence and young adulthood, his or her fantasied infantile omnipotence in exchange for a sexual identity of - in these-described terms - a 'man' or a 'woman'. It would be like having to accept only certain dispensations as well as salvageable sights, if ony to see the whole fabric ruined into the bargin. A person cannot deeply accept an adult sexual identity until he has been able to find that this identity can express all the feeling-potentialities of his comparatively boundless infancy. This implies that he has become able to blend, for example, his infantile - dependent needs into his more adult erotic strivings, than regard these as mutually exclusive in the way that the mother of the future patient or the persons infant frighteningly feels that her lust has been placed in her mothering. Another difficult facet of this situation resides in a patient's youngful conviction, based on his intrafamiliar experiences, which he can win parental love only if he can become or, perhaps, at an unconscious level remain - a girl; accepting her sexuality as a woman is equated with the abandonment of the hope of being loved.
Concerning the warped experiences their persons have and with the oedipal phase of development, calls to our attention of two features. First, the child whose parents are more narcissistic than truly object-related in faced with the basically hopeless challenge of trying to compete with the mother's own narcissistic love for herself, and with the father's similar love for himself, than being presented with a competitive challenge involving separate, flesh-and-blood human beings. Secondly, concerning warped oedipal experiences, in, as far as the parents succeeded in achieving object-relatedness, this has often become only weakly established as a genital level, so that it remains much more prominently at the mother-infant level of ego-development. Thus, the mother, for example, is much more able to love her infant son than her adult husband, and the oedipal competition between husband and son are in terms of who can better become, or remain, the infant whom the mother is capable of loving. When the infant becomes chronologically a young man, having learned that one wins a woman not through genial assertiveness but through regression, he is apt to shy away from entering into true adult genitality, and is tempted to settle for what amounts to 'regressive victory' in the oedipal struggle
We write much about the analyst’s or therapist’s being able to identify or empathize with the patient for helping in the resolution of the neurotic or psychotic difficulties. Such writings always portray a merely transitory identification, an empathic sensing of the patient’s conflicts, an identification that is of essentially communicative value only. However, it should be seen that we inevitably identify with the patient another fashion also, we identify with the healthy elements in him, in a way that entails enduing, constructive additions to our own personality. Patients - above all schizophrenic patients - need and welcome our acknowledgement, simply and undemonstratively, that they have contributed, and are contributing, in some such significant way, to our existence.
Increasing maturity involves increasing ability not merely to embrace change in the world around one, but to realize that one is oneself in a constant state of change. By contrast, the recovering, maturing patiently becomes less and less dependent upon any such sharply delineated, static self-image or even a constellation of such images, the answer to the question, “Who are you?” is almost as small, solid, and well defined as a stone, but is a larger, fluid, richly-laden, and sniffingly outlined as an ocean? As the individual becomes well, he comes to realize that, as Henri Bergson (1944) puts it, “reality is a perpetual growth, a creation pursued without end. . . . A perpetual becoming,” and to the extent that he can actively welcome change and let it become part of him, he comes to know that - again in Bergson’s phrase - “to exist is to change, to change is too mature, to mature is to go on creating oneself endlessly.”
Philosophical issues about ‘perception’ tend to be issues specifically about ‘sense-perception’. In England (and the same is true of comparable terms in many other languages) the term ‘perception’ has a wider connotation than anything that has to do with the senses and sense-organs, though it generally involves the idea of what may imply, if only in a metaphorical sense, a point of view. Thus it is now increasingly common for news-commentators, for example, to speak of events, even though those people have not been witnesses of them. In one sense, however, therre is nothing new about this, in seventeenth-and-eighteenth-century philosophical usage, words for perception were used with a much wider coverage than sense-perception alone. It is, however, sense-perception that has typically raised the largest and most obvious philosophical problems.
Such problems may be said to fall into two categories. These are, forst, the epistemological problems about the role of sense-perception in connection with the acquisition and possession of knowledge of the world around us. These problems - does perception give us knowledge of the so-called ‘external world’, and to what extent? - have become dominant in epistemology since Descartes because of his invocation of the method of doubt, although they undoubtedly existed in philosophers’ minds in one way or another before that. In early and middle twentieth-century Anglo-Saxon philosophy such problems centred on the question whether there are firm data provided by the senses - so-called sense-data - and if so what is the relation of such sense-data to so-called material objects. Such problems are not essentially problems for the philosophy of mind, although certain answers to questions about perception which undoubtedly belong to the philosophy of mind can certainly add to epistemological differences. If perception is assimilated, for example, to sensation, there is an obvious temptation to think that in perception we are restricted, at any rate initially, to the contents of our own minds.
The second category of problems about perception - those that fall directly under the heading of the philosophy of mind - are thus in a sense prior to the problems that exercised many empiricist in the first half of this century. They are problems about how perception is to be construed and how it relates to a number of other aspects of the mind’s functioning - sensations, concepts and other things involved in our understanding of things, beliefs and judgements, and the imagination, our action in relation to the world around us, and the causal processes involved in the physics, biology and psychology of perception. Some of the last were central to the considerations that Aristotle raised about perception in his ‘De Anima’.
It is obvious enough that sense-perception involves some kind of stimulation of sense organs by stimuli that are themselves the product of physical processes which are biological in character are then initiated. Moreover, only if the organism in which this takes place is adapted to such excitation, for which the stimulation can perception ensue. Aristotle had something to say about such matters, but it was evident to him that such an account was insufficient to explain what perception itself is. It might be thought that the most obvious thing is missing in such an account is some reference to consciousness. But while it may be the case that perception can take place only in creatures that have consciousness in some sense, it is not clear that every case of perception directly involves consciousness. There is such a thing as unconscious perception and psychologists have recently drawn attention to the phenomenon which is described as ‘blind-sight’ - an ability, generally manifested in patients with certain kinds of brain-damage, to discriminate sources of light, even when the people concerned have no consciousness of the lights and think that they are guessing about them. It is important, then, not to confuse the plausible claim that perception can take place only in conscious beings with the less plausible claim that perception always involves consciousness of objects. A similar point may apply to the relation of perception to some of the other items exposed to concept-possession.
Consciousness may possibly be the most challenging and persuasive source of problems in the whole of philosophy. Our own consciousness seems to be the most basic fact confronting us, yet it is almost impossible to say what consciousness is. Is mine like yours? Is ours like that of animals? Might machines come to have consciousness? Is it possible for there to be disembodied consciousness? Whatever complex biological and neural processes go on back-stage, it is my consciousness that provides the theatre where my experiences and thoughts have their existence, where my desires are felt and where my intentions are formed. But then how am I to conceive that ‘I’, or ‘self’ that is the spectator, or at any rate the owner of this theatre? There problems together make up what is sometimes called ‘the hard problem’ of consciousness. One of the difficulties in thinking about consciousness is that the problems seem bnot to be scientific ones. Gottfried Wilhelm Leibniz (1646-1716) remarked that if we could construct a field or machine, per se, and find to its expansive area, we still would not be able to find consciousness, so that consciousness resides in simple subjects, not complex ones. Even if we are convinced that consciousness somehow emerges from the complexity of brain functioning, we may still feel baffled about the way the emergence takes place, or why it takes place in just the way it does.
The nature of conscious experience has been the largest single obstacle to physicalism, behaviourism and functionalism in the philosophy of mind: These are all views that according to their opponents, can only be believed by feigning permanent anaesthesia. But many philosophers are convinced that we can divide and conquer: We may make progress not by thinking of one ‘hard’ problem, but by breaking the subject up into different skills and recognizing that rather than a single self or observer we would do better to think of a relatively undirected whirl of cerebral activity, with no inner theatre, no inner lights, and above all no inner spectator.
Til most recently it has been thought that in the study of how nerve cells, or neurons, receives and transmits information. Two types of phenomena are involved in processing nerve signals: Electrical and chemical. Electrical events propagate a signal within a neuron, and chemical processes transmit the signal from one neuron to another neuron or to a muscle cell.
A neuron is a long cell that has a thick central area containing the nucleus, it also has one long process called an axon and one or more short, bushy processes called dendrites. Dendrites receive impulses from other neurons. (The exceptions are sensory neurons, such as those that transmit information about temperature or touch, in which the signal is generated by specialized receptors in the skin.) These impulses are propagated electrically along the cell membrane to the end of the axon. At the tip of the axon the signal is chemically transmitted to an adjacent neuron or muscle cell.
Like all other cells, neurons contain charged ions: Potassium and sodium (positively charged) and chlorine (negatively charged). Neurons differ from other cells in that they can produce a nerve impulse. A neuron is polarized - that is, it has an overall negative charge inside the cell membrane because of the high concentration of chlorine ions and low concentration of potassium and sodium ions. The concentration of these same ions is exactly reversed outside the cell. This charge differential represents stored electrical energy, sometimes called membrane potential or resting potential. The negative charge inside the cell is maintained by two features. The first is the selective permeability of the cell membrane, which is more permeable to potassium than sodium. The second feature is sodium pumps within the cell membrane that actively pump sodium out of the cell. When depolarization occurs, this charge differential across the membrane is reversed, and a nerve impulse is produced.
Depolarization is a rapid change in the permeability of the cell membrane. When sensory information or any other kind of stimulating current is received by the neuron, the membrane permeability is changed, allowing a sudden influx of sodium ions into the cell. The high concentration of sodium, or action potential, changes the overall charges within the cell from negative too positively. The local changes in ion concentration triggers similar reactions along the membrane, propagating the nerve impulse. After a brief period called the refractory period, during which the ionic concentration returned to resting potential, the neuron can repeat this process. Nerve impulses travel at different speeds, depending on the cellular composition of a neuron. Where speed of impulse is important, as in the nervous system, axons are insulated with a membranous substance called myelin. The insulation provided by myelin maintains the ionic charge over long distances. Nerve impulses are propagated at specific points along the myelin sheath; These points are called the nodes of Ranvier. Examples of myelinated axons are those in sensory nerve fibers and nerves connected to skeletal muscles. In non-myelinated cells, the nerve impulse is propagated more diffusely.
When the electrical signal reaches the tip of an axon, it stimulates small presynaptic vesicles in the cell. These vesicles contain chemicals called neurotransmitters, which are released into the microscopic space between neurons (the synaptic cleft). The neurotransmitter attaches on the surface of the adjacent neuron. This stimulus causes the adjacent cell to depolarize and propagate an action potential of its own. The duration of a stimulus from a neurotransmitter is limited by the breakdown of the chemicals in the synaptic cleft and the reuptake by the neuron that produced them. Formerly, each neuron was thought to make only one transmitter, but recent studies have shown that some cells make two or more.
During the early 1900s, in examining the workings of the nervous system, physiologists were beginning to explore the idea that the transmission of nerve impulses takes place, in part, via chemical means. Loewi decided to explore this idea. During a stay in London in 1903, he met Sir Dale, who was also interested in the chemical transmission of nerve impulses. However, for Loewi, Dale, and all the other researchers pursuing a chemical transmitter of nerve impulses, years of effort produced no solid evidence. In 1921 Loewi suspended two frogs' hearts in solution, one with a major nerve removed. Removing fluid from the heart that still contained the nerve, and injecting the fluid into the nerveless heart, Loewi observed that the second heart behaved as if the missing nerve were present. The nerves, he concluded, do not act directly on the heart - it is the action of chemicals, freed by the stimulation of nerves, that causes increases in heart rate and other functional changes. In 1926 Loewi and his colleagues identified one of the chemicals in his experiment as acetylcholine. This was indisputably a neurotransmitter - a chemical that serves to transmit nerve impulses in the involuntary nervous system.
We acknowledge the neurotransmitters are inherently made by chemically induced neurons, or nerve cells. Neurons send out neurotransmitters as chemical signals to activate or inhibit the function of neighboring cells.
Within the central nervous system, which consists of the brain and the spinal cord, neurotransmitters pass from neuron to neuron. In the peripheral nervous system, which is made up of the nerves that run from the central nervous system to the rest of the body, the chemical signals pass between a neuron and an adjacent muscle or gland cells.
Chemical compounds - belonging to three chemical families - are widely recognized as neurotransmitters. In addition, certain other body chemicals, including adenosine, histamine, enkephalins, endorphins, and epinephrine, have neurotransmitterlike properties. Experts believe that there are many more neurotransmitters yet undiscovered.
The first of the three families is composed of amines, a group of compounds containing molecules of carbon, hydrogen, and nitrogen. Among the amine neurotransmitters are acetylcholine, norepinephrine, dopamine, and serotonin. Acetylcholine is the most widely used neurotransmitter in the body, and neurons that leave the central nervous system (for example, those running to skeletal muscle) use acetylcholine as their neurotransmitter; neurons that run to the heart, blood vessels, and other organs may use acetylcholine or norepinephrine. Dopamine is involved in the movement of muscles, and it controls the secretion of the pituitary hormone prolactin, which triggers milk production in nursing mothers.
The second neurotransmitter family is composed of amino acids, organic compounds containing both an amino group (NH2) and a carboxylic acid group (COOH). Amino acids that serve as neurotransmitters include glycine, glutamic and aspartic acids, and gamma-amino butyric acid (GABA). Glutamic acid and GABA are the most abundant neurotransmitters within the central nervous system, and especially in the cerebral cortex, which is largely responsible for such higher brain functions as thought and interpreting sensations.
The third neurotransmitter family is composed of peptides, which are compounds that contain at least two, and sometimes as many as 100 amino acids. Peptide neurotransmitters are poorly understood, but scientists know that the peptide neurotransmitter called substance P influences the sensation of pain.
Overall, each neuron uses only a single compound as its neurotransmitter. However, some neurons outside the central nervous system can release both an amine and a peptide neurotransmitter.
Neurotransmitters are manufactured from precursor compounds like amino acids, glucose, and the dietary amine-called choline. Neurons modify the structure of these precursor compounds in a series of reactions with enzymes. Neurotransmitters that comes from amino acids include serotonin, for which it is derived from tryptophan. Dopamine and norepinephrine, under which are derived from tyrosine, and glycine, which is derived from threonine. Among the neurotransmitters made from glucose are glutamate, aspartate, and GABA. The choline serves as the precursor for acetylcholine
Neurotransmitters are released into a microscopic gap, called a synapse, that separates the transmitting neuron from the cell receiving the chemical signal. The cell that generates the signal is called the presynaptic cell, while the receiving cell is termed the postsynaptic cell.
After their release into the synapse, neurotransmitters combine chemically with highly specific protein molecules, termed receptors, embedded in the surface membranes of the postsynaptic cell. When this combination occurs, the voltage, or electrical force, of the postsynaptic cell is either increased (excited) or decreased (inhibited).
When a neuron is in its resting state, its voltage is about -70 millivolts. An excitatory neurotransmitter alters the membrane of the postsynaptic neuron, making it possible for ions (electrically charged molecules) to move back and forth across the neuron’s membranes. This flow of ions makes the neuron’s voltage rise toward zero. If enough excitatory receptors have been activated, the postsynaptic neuron responds by firing, generating a nerve impulse that causes its own neurotransmitter to be released into the next synapse. An inhibitory neurotransmitter causes different ions to pass back and forth across the postsynaptic neuron’s membrane, lowering the nerve cell’s voltage to -80 or -90 millivolts. The drop in voltage makes it less likely that the postsynaptic cell will fire.
If the postsynaptic cell is a muscle cell rather than a neuron, an excitatory neurotransmitter will cause the muscle to contract. If the postsynaptic cell is a gland cell, an excitatory neurotransmitter will cause the cell to secrete its contents.
While most neurotransmitters interact with their receptors to create new electrical nerve impulses that energize or inhibit the adjoining cell, some neurotransmitter interactions do not generate or suppress nerve impulses. Instead, they interact with a second type of receptor that changes the internal chemistry of the postsynaptic cell by either causing or blocking the formation of chemicals called second messenger molecules. These second messengers regulate the postsynaptic cell’s biochemical processes and enable it to conduct the maintenance necessary to continue synthesizing neurotransmitters and conducting nerve impulses. Examples of second messengers, which are formed and entirely contained within the postsynaptic cell, include cyclic adenosine monophosphate, diacylglycerol, and inositol phosphates.
Once neurotransmitters have been secreted into synapses and have passed on their chemical signals, the presynaptic neuron clears the synapse of neurotransmitter molecules. For example, acetylcholine is broken down by the enzyme acetylcholinesterase into choline and acetate. Neurotransmitters like dopamine, serotonin, and GABA is removed by a physical process called reuptake. In reuptake, a protein in the presynaptic membrane acts as a sort of sponge, causing the neurotransmitters to reenter the presynaptic neuron, where they can be broken down by enzymes or repackaged for reuse.
Neurotransmitters are known to be involved in many disorders, including Alzheimer’s disease. Victims of Alzheimer’s disease suffer from loss of intellectual capacity, disintegration of personality, mental confusion, hallucinations, and aggressive - even violent - behavior. These symptoms are the result of progressive degeneration in many types of neurons in the brain. Forgetfulness, one of the earliest symptoms of Alzheimer’s disease, is partly caused by the destruction of neurons that normally release the neurotransmitter acetylcholine. Medications that increase brain levels of acetylcholine have helped restore short-term memory and reduce mood swings in some Alzheimer’s patients.
Neurotransmitters also play a role in Parkinson disease, which slowly attacks the nervous system, causing symptoms that worsen over time. Fatigue, mental confusion, a masklike facial expression, stooping posture, shuffling gait, and problems with eating and speaking are among the difficulties suffered by Parkinson victims. These symptoms have been partly linked to the deterioration and eventual death of neurons that run from the base of the brain to the basal ganglia, a collection of nerve cells that manufacture the neurotransmitter dopamine. The reasons why such neurons die are yet to be understood, but the related symptoms can be alleviated. L-dopa, or levodopa, widely used to treat Parkinson disease, acts as a supplementary precursor for dopamine. It causes the surviving neurons in the basal ganglia to increase their production of dopamine, by that compensating to some extent for the disabled neurons.
Many other effective drugs have been shown to act by influencing neurotransmitter behavior. Some drugs work by interfering with the interactions between neurotransmitters and intestinal receptors. For example, belladonna decreases intestinal cramps in such disorders as irritable bowel syndrome by blocking acetylcholine from combining with receptors. This process reduces nerve signals to the bowel wall, which prevents painful spasms.
Other drugs block the reuptake process. One well-known example is the drug fluoxetine (Prozac), which blocks the reuptake of serotonin. Serotonin then remains in the synapse for a longer time, and its ability to act as a signal is prolonged, which contributes to the relief of depression and the control of obsessive-compulsive behaviors.
Dopamine, chemical known as a neurotransmitter essential to the functioning of the central nervous system. During neurotransmission, dopamine is transferred from one nerve cell, or neuron, to another, playing a key role in brain function and human behavior.
Dopamine forms from a precursor molecule called dopa, which is manufactured in the liver from the amino acid tyrosine. Dopa is then transported by the circulatory system to neurons in the brain, where the conversion to dopamine takes place.
Dopamine is a versatile neurotransmitter. Among its many functions, it plays a major role in two activities of the central nervous system: one that helps control movement, and a second that are strongly associated with emotion-based behaviors.
The pathway involved in movement control is called the nigrostriatal pathway. Dopamine is released by neurons that originate from an area of the brain called the substantia nigra and connect to the part of the brain known as the corpora striata, an area known to be important in controlling the musculoskeletal system.
The second brain pathway in which dopamine plays a major role is called the mesocorticolimbic pathway. Neurons in an area of the brain called the ventral tegmentalarea transmits dopamine to other neurons connected to various parts of the limbic system, which is responsible for regulating emotion, motivation, behavior, the sense of smell, and variously autonomic, or involuntary, functions like heartbeat and breathing.A growing body of evidence suggests that dopamine be involved in several major brain disorders. Narcolepsy, a disorder characterized by brief, recurring episodes of sudden, deep sleep, is associated with abnormally high levels of both dopamine and a second neurotransmitter, acetylcholine. Huntington’s chorea, an inherited, fatal illness in which neurons in the base of the brain are progressively destroyed, is also linked to an excess of dopamine.
Commonly known as shaking palsy, Parkinson disease is another brain disorder in which dopamine is involved. Besides tremors of the limbs, Parkinson patients suffer from muscular rigidity, which leads to difficulties in walking, writing, and speaking. This disorder results from the degeneration and death of neurons in the nigrostriatal pathway, resulting in low levels of dopamine. The symptoms of Parkinson disease can be reduced by treatment with a drug called levodopa, or L-dopa, which converts to dopamine in the brain.
Schizophrenia is a psychiatric disorder characterized by loss of contact with reality and major changes in personality. Schizophrenics have normal levels of dopamine in the brain, but because they are highly sensitive to this neurotransmitter, these normal levels of dopamine triggers unusual behaviors. Drugs such as thorazine that blocks the action of dopamine have been found to decrease the symptoms of schizophrenia.
Studies suggest that people who are addicted to alcohol and other drugs like, cocaine and nicotine have less dopamine in the mesocorticolimbic pathway. These drugs appear to increase dopamine levels, resulting in the pleasurable feelings associated with the drugs.
Serotonin, neurotransmitter, or chemical that transmits messages across the synapses, or gaps, between adjacent cells. Among its many functions, serotonin is released from blood cells called platelets to activate blood vessel constriction and blood clotting. In the gastrointestinal tract, serotonin inhibits gastric acid production and stimulates muscle contraction in the intestinal wall. Its functions in the central nervous system and effects on human behavior - including mood, memory, and appetite control - have been the subject of a great deal of research. This intensive study of serotonin has revealed important knowledge about the serotonin-related cause and treatment of many illnesses.
Serotonin is produced in the brain from the amino acid tryptophan, which is derived from foods high in protein, such as meat and dairy products. Tryptophan is transported to the brain, where it is broken down by enzymes to produce serotonin. During neurotransmission, serotonin is transferred from one nerve cell, or neuron, to another, triggering an electrical impulse that stimulates or inhibits cell activity as needed. Serotonin is then reabsorbed by the first neuron, in a process known as reuptake, where it is recycled and used again or converted into an inactive chemical form and excreted.
While the complete picture of serotonin’s function in the body is still being investigated, many disorders are known to be associated with an imbalance of serotonin in the brain. Drugs that manipulate serotonin levels have been used to alleviate the symptoms of serotonin imbalances. Some of these drugs, known as selective serotonin reuptake inhibitors (SSRIs), block or inhibit the reuptake of serotonin into neurons, enabling serotonin to remain active in the synapses for a longer period. These medications are used to treat such psychiatric disorders as depression; Obsessive-compulsive disorder, in which repetitive and disturbing thoughts trigger bizarre, ritualistic behaviors, and impulsive aggressive behaviors. Fluoxetine (more commonly known by the brand name Prozac), is a widely prescribed SSRI used to treat depression, and more recently, obsessive-compulsive disorder.
Drugs that affect serotonin levels may prove beneficial in the treatment of nonpsychiatric disorders as well, including diabetic neuropathy (degeneration of nerves outside the central nervous system in diabetics) and premenstrual syndrome. Recently the serotonin-releasing agent dexfenfluramine has been approved for patients who are 30 percent or more over their ideal body weight. By preventing serotonin reuptake, dexfenfluramine promotes satiety, or fullness, after eating less food.
Other drugs serve as agonists that react with neurons to produce effects similar to those of serotonin. Serotonin agonists have been used to treat migraine headaches, in which low levels of serotonin cause arteries in the brain to swell, resulting in a headache. Sumatriptan is an agonist drug that mimics the effects of serotonin in the brain, constricting blood vessels and alleviating pain.
Drugs known as antagonists bind with neurons to prevent serotonin neurotransmission. Some antagonists have been found effective in treating the nausea that typically accompanies radiation and chemotherapy in cancer treatment. Antagonists are also being tested to treat high blood pressure and other cardiovascular disorders by blocking serotonin’s ability to constrict blood vessels. Other antagonists may produce an effect on learning and memory in age-associated memory impairment.
The Synapse is the signal conveying everything that human beings sense and think, and every motion they make, follows nerve pathways in the human body as waves of ions (atoms or groups of atoms that carries electric charges). Australian physiologist Sir John Eccles discovered many intricacies of this electrochemical signaling process, particularly the pivotal step in which a signal is conveyed from one nerve cell to another. He shared the 1963 Nobel Prize in physiology or medicine for this work, which he described in a 1965 Scientific American article.
How does one nerve cell transmit the nerve impulse to another cell? Electron microscopy and other methods show that it does so by means of special extensions that deliver a squirt of transmitter substance
The human brain is the most highly organized form of matter known, and in complexity the brains of the other higher animals are not greatly inferior. For certain purposes regarding the brain for being analogous to a machine is expedient. Even if it is so regarded, however, it is a machine of a totally different kind from those made by man. In trying to understand the workings of his own brain man meets his highest challenge. Nothing is given; There are no operating diagrams, no maker's instructions.
The first step in trying to understand the brain is to examine its structure to discover the components from which it is built and how they are related to each another. After that one can attempt to understand the mode of operation of the simplest components. These two modes of investigation - the morphological and the physiological - have now become complementary. In studying the nervous system with today's sensitive electrical device, however, finding physiological events that cannot be correlated with any known anatomical structure is all too easy. Conversely, the electron microscope reveals many structural details whose physiological significance is obscure or unknown.
At the close of the past century the Spanish anatomist Santiago Ramón Cajal showed how all parts of the nervous system are built up of individual nerve cells of many different shapes and sizes. Like other cells, each nerve cell has a nucleus and the surrounding cytoplasm. Its outer surface consists of many fine branches - the dendrites - that receive nerve impulses from other nerve cells, and one relatively long branch - the axon - that transmits nerve impulses. Near its end the axon divides into branches that end at the dendrites or bodies of other nerve cells. The axon can be as short as a fraction of a millimeter or if a meter, depending on its place and function. It has many properties of an electric cable and is uniquely specialized to conduct the brief electrical waves called nerve impulses. In very thin axons these impulses travel at less than one meter per second; In others, for example in the large axons of the nerve cells that activate muscles, they travel as fast as 100 meters per second.
The electrical impulse that travels along the axon ceases abruptly when it comes to the point where the axon's terminal fibers contact another nerve cell. These junction points were given the name "synapses" by Sir Charles Sherrington, who laid the foundations of what is sometimes called synaptology. If the nerve impulse is to continue beyond the synapse, it must be regenerated afresh on the other side. As recently as 15 years ago some physiologists held that transmission at the synapse was predominantly, if not exclusively, an electrical phenomenon. Now, however, there is abundant evidence that transmission is made by the release of specific chemical substances that trigger a regeneration of the impulse. In fact, the first strong evidence showing that some transmitter substance act across the synapse was provided more than 40 years ago by Sir Henry Dale and Otto Loewi.
It has been estimated that the human central nervous system, which of course includes the spinal cord and the brain itself, consists of about 10 billion (1010) nerve cells. With rare exceptions each nerve cell receives information directly as impulses from many other nerve cells - often hundreds - and transmits information to a like number. Depending on its threshold of response, a given nerve cell may fire an impulse when stimulated by only a few incoming fibers or it may not fire until stimulated by many incoming fibers. It has long been known that this threshold can be raised or lowered by various factors. Moreover, it was supposed some 60 years ago that some incoming fibers must inhibit the firing of the receiving cell rather than excite it. The conjecture was subsequently confirmed, and the mechanism of the inhibitory effect has now been clarified. This mechanism and its equally fundamental counterpart - nerve-cell excitation - are of its topic.
In the levels of anatomy there are some clues to show how the fine axon terminals impinging on a nerve cell can make the cell regenerate a nerve impulse of its own nerve cell and its dendrites are covered by fine branches of nerve fibers that end in knob-like structures. These structures are the synapses.
The electron microscope has revealed structural details of synapses that fit in nicely with the view that a chemical transmitter is involved in nerve transmission. Enclosed in the synaptic knob are many vesicles, or tiny sacs, which appear to contain the transmitter substances that induce synaptic transmission. Between the synaptic knob and the synaptic membrane of the adjoining nerve cell is a remarkably uniform space of about 20 millimicrons that is termed the synaptic cleft. Many of the synaptic vesicles are concentrated adjacent to this cleft; It seems plausible that the transmitter substance is discharged from the nearest vesicles into the cleft, where it can act on the adjacent cell membrane. This hypothesis is supported by the discovery that the transmitter is released in packets of a few thousand molecules.
The study of synaptic transmission was revolutionized in 1951 by the introduction of delicate techniques for recording electrically from the interior of single nerve cells. This is done by inserting into the nerve cell an extremely fine glass pipette with a diameter of .5 microns - about a fifty-thousandth of an inch. The pipette is filled with an electrically conducting salt solution such as concentrated potassium chloride. If the pipette is carefully inserted and held rigidly in place, the cell membrane appears to seal quickly around the glass, thus preventing the flow of a short-circuiting current through the puncture in the cell membrane. Impaled in this fashion, nerve cells can function normally for hours. Although there is no way of observing the cells during the insertion of the pipette, the insertion can be guided by using as clues the electric signals that the pipette picks up when close to active nerve cells.
At the John Curtin School of Medical Research in Canberra first employed this technique, choosing to study the large nerve cells called motoneurons, which lie in the spinal cord whose function is to activate muscles. This was a fortunate choice: Intracellular investigations with motoneurons are easier and more rewarding than those with any other kind of mammalian nerve cell.
Finding that when the nerve cell responds to the chemical synaptic transmitter, the response depends in part on characteristic features of ionic composition that are also concerned with the transmission of impulses in the cell and along its axon. When the nerve cell is at rest, its physiological makeup resembles that of most other cells in that the water solution inside the cell is quite different in composition from the solution in which the cell is bathed. The nerve cell can exploit this difference between external and internal composition and use it in quite different ways for generating an electrical impulse and for synaptic transmission.
The composition of the external solution is well established because the solution is essentially the same as blood from which cells and proteins have been removed. The composition of the internal solution is known only approximately. Indirect evidence suggests that the concentrations of sodium and chloride ions outside the cell are respectively some 10 and 14 times higher than the concentrations inside the cell. In contrast, the concentration of potassium ions inside the cell is about 30 times higher than the concentration outside.
How can one account for this remarkable state of affairs? Part of the explanation is that inside the cell is negatively charged with the respect of the cell about 70 millivolts. Since like charges repel each other, this internal negative charge tends to drive chloride ions (Cl-) outward through the cell membrane and, at the same time, to impede their inward movement. In fact, a potential difference of 70 millivolts is just sufficient to maintain the observed disparity in the concentration of chloride ions inside the cell and outside it; Chloride ions diffuse inward and outward at equal rates. A drop of 70 millivolts across the membrane therefore defines the "equilibrium potential" for chloride ions.
To obtain a concentration of potassium ions (K) that is 30 times higher inside the cell than outside would require that the interior of the cell membrane be about 90 millivolts negative with respect to the exterior. Since the actual interior is only 70 millivolts negative, it falls short of the equilibrium potential for potassium ions by 20 millivolts. Evidently the thirtyfold concentration can be achieved and maintained only if there is some auxiliary mechanism for "pumping" potassium ions into the cell at a rate equal to their spontaneous net outward diffusion.
The pumping mechanisms have fewer, but more difficult tasks of pumping sodium ions (Na) out of the cell against a potential gradient of 130 millivolts. This figure is obtained by adding the 70 millivolts of internal negative charge to the equilibrium potential for sodium ions, which is 60 millivolts of internal positive charge. If it were not for this postulated pump, the concentration of sodium ions inside and outside the cell would be almost the reverse of what is observed.
In their classic studies of nerve-impulse transmission in the giant axon of the squid, A. L. Hodgkin, A. F. Huxley and Bernhard Katz of Britain proved that the propagation of the impulse coincides with abrupt changes in the permeability of the axon membrane. When a nerve impulse has been triggered in some way, what can be described as a gate opens and lets sodium ions pour into the axon during the advance of the impulse, making the interior of the axon locally positive. The process is self-reinforcing in that the flow of some sodium ions through the membrane opens the gate further and makes it easier for others to follow. The sharp reversal of the internal polarity of the membrane makes up the nerve impulse, which moves like a wave until it has traveled the length of the axon. In the wake of the impulse the sodium gate closes and a potassium gate opens, by that restoring the normal polarity of the membrane within a millisecond or less.
With this understanding of the nerve impulse in hand, one is ready to follow the electrical events at the excitatory synapse. One might guess that if the nerve impulse results from an abrupt inflow of sodium ions and a rapid change in the electrical polarity of the axon's interior, something similar must happen at the body and dendrites of the nerve cell in order to generate the impulse in the first place. Indeed, the function of the excitatory synaptic terminals on the cell body and its dendrites is to depolarize the interior of the cell membrane essentially by permitting an inflow of sodium ions. When the depolarization reaches a threshold value, a nerve impulse is triggered.
As a simple instance of this phenomenon we have recorded the depolarization that occurs in a single motoneuron activated directly by the large nerve fibers that enter the spinal cord from special stretch-receptors known as annulospiral endings. These receptors in turn are found in the same muscle that is activated by the motoneuron under study. Thus the whole system forms a typical reflex arc, such as the arc responsible for the patellar reflex, or "knee jerk."
To conduct the experiment we anesthetize an animal (most often a cat) and free by dissection a muscle nerves that contains these large nerve fibers. By applying a mild electric shock to the exposed nerve one can produce a single impulse in each of the fibers; Since the impulses travel to the spinal cord almost synchronously, they are referred to collectively as a volley. The number of impulses contained in the volley can be reduced by reducing the stimulation applied to the nerve. The volley strength is measured at a point just outside the spinal cord and is displayed on an oscilloscope. About half a millisecond after detection of a volley there is a wavelike change in the voltage inside the motoneuron that has received the volley. The change is detected by a microelectrode inserted in the motoneuron and is displayed on another oscilloscope.
What we find is that the negative voltage inside the cell becomes progressively fewer negative as more of the fibers impinging on the cell are stimulated to fire. This observed depolarization is in fact a simple summation of the depolarizations produced by each individual synapse. When the depolarization of the interior of the motoneuron reaches a critical point, a "spike" suddenly appears on the second oscilloscope, showing that a nerve impulse has been generated. During the spike the voltage inside the cell changes from about 70 millivolts negative to as much as 30 millivolts positive. The spike regularly appears when the depolarization, or reduction of membrane potential, reaches a critical level, which is usually between 10 and 18 millivolts. The only effect of a further strengthening of the synaptic stimulus is to shorten the time needed for the motoneuron to reach the firing threshold. The depolarizing potentials produced in the cell membrane by excitatory synapses are called excitatory postsynaptic potentials, or EPSP's.
Through one barrel of a double-barreled microelectrode one can apply a background current to change the resting potential of the interior of the cell membrane, either increasing it or decreasing it. When the potential is made more negative, the EPSP rises more steeply to an earlier peak. When the potential is made less negative, the EPSP rises more slowly to a lower peak. Finally, when the charge inside the cell is reversed so as to be positive with respect to the exterior, the excitatory synapses give rise to an EPSP that is actually the reverse of the normal one.
These observations support the hypothesis that excitatory synapses produce what amounts virtually to a short circuit in the synaptic membrane potential. When this occurs, the membrane no longer acts as a barrier to the passage of ions but lets them flow through in response to the differing electric potential on the two sides of the membrane. In other words, the ions are momentarily allowed to travel freely down their electrochemical gradients, which means that the sodium ions flow into the cell and, to a lesser degree, potassium ions flow out. It is this net flow of positive ions that creates the excitatory postsynaptic potential. The flow of negative ions, such as the chloride ion, is apparently not involved. By artificially altering the potential inside the cell one can establish that there is no flow of ions, and therefore no EPSP, when the voltage drop across the membrane is zero.
How is the synaptic membrane converted from a strong ionic barrier into an ion-permeable state? It is currently accepted that the agency of conversion is the chemical transmitter substance contained in the vesicles inside the synaptic knob. When a nerve impulse reaches the synaptic knob, some of the vesicles are caused to eject the transmitter substance into the synaptic cleft. The molecules of the substance would take only a few microseconds to diffuse across the cleft and become attached to specific receptor sites on the surface membrane of the adjacent nerve cell.
Presumably the receptor sites are associated with fine channels in the membrane that are opened in some way by the attachment of the transmitter-substance molecules to the receptor sites. With the channels thus opened, sodium and potassium ions flow through the membrane thousands of times more readily than they normally do, by that producing the intense ionic flux that depolarizes the cell membrane and produces the EPSP. In many synapses the current flows strongly for only about a millisecond before the transmitter substance is eliminated from the synaptic cleft, either by diffusion into the surrounding regions or as a result of being destroyed by enzymes. The latter process is known to occur when the transmitter substance is acetylcholine, which is destroyed by the enzyme acetylcholinesterase.
The substantiation of this general picture of synaptic transmission requires the solution of many fundamental problems. Since we do not know the specific transmitter substance for the vast majority of synapses in the nervous system, we do not know whether there are many different substances or only a few. The only one identified with reasonable certainty in the mammalian central nervous system is acetylcholine. We know practically nothing about the mechanism by which a presynaptic nerve impulse causes the transmitter substance to be injected into the synaptic cleft. Nor do we know how the synaptic vesicles not immediately next to the synaptic cleft follow to moved up to the firing line to replace the emptied vesicles. It is supposed that the vesicles contain the enzyme systems needed to recharge themselves. The entire process must be swift and efficient: The total amount of transmitter substance in synaptic terminals is enough for only a few minutes of synaptic activity at normal operating rates. There are also knotty problems to be solved on the other side of the synaptic cleft. What, for example, is the nature of the receptor sites? How are the ionic channels in the membrane opened?
The second type of synapse that has been identified in the nervous system. These are the synapses that can inhibit the firing of a nerve cell even though it may be receiving a volley of excitatory impulses. When inhibitory synapses are examined in the electron microscope, they look very much like excitatory synapses. (There are probably some subtle differences, but they need not concern us here.) Microelectrode recordings of the activity of single motoneurons and other nerve cells have now shown that the inhibitory postsynaptic potential (IPSP) is virtually a mirror image of the EPSP. Moreover, individual inhibitory synapses, like excitatory synapses, have a cumulative effect. The chief difference is simply that the IPSP makes the cell's internal voltage more negative than it is normally, which is in a direction opposite to that needed for generating a spike discharge.
By driving the internal voltage of a nerve cell in the negative direction inhibitory synapses oppose the action of excitatory synapses, which of course drive it in the positive direction. So if the potential inside a resting cell is 70 millivolts negative, a strong volley of inhibitory impulses can drive the potential to 75 or 80 millivolts depreciating count. One can easily see that if the potential is made more negative in this way the excitatory synapses find it more difficult to raise the internal voltage to the threshold point for the generation of a spike. Thus, the nerve cell responds to the algebraic sum of the internal voltage changes produced by excitatory and inhibitory synapses.
If, as in the experiment described earlier, the internal membrane potential is altered by the flow of an electric current through one barrel of a double-barreled microelectrode, one can observe the effect of such changes on the inhibitory postsynaptic potential. When the internal potential is made less negative, the inhibitory postsynaptic potential is deepened. Conversely, when the potential is made more negative, the IPSP diminishes; it finally reverses when the internal potential is driven below minus 80 millivolts.
One can therefore assume that inhibitory synapse’s share with excitatory synapses the ability to change the ionic permeability of the synaptic membrane. The difference is that inhibitory synapses enable ions to flow freely down an electrochemical gradient that has an equilibrium point at minus 80 millivolts rather than at zero, as is the case for excitatory synapses. This effect could be achieved by the outward flow of positively charged ions such as potassium or the inward flow of negatively charged ions such as chloride, or by a combination of negative and positive ionic flows such that the interior reaches equilibrium at minus 80 millivolts.
If the concentration of chloride ions within the cell is increased as much as three times, the inhibitory postsynaptic potential reverses and acts as a depolarizing current; that is, it resembles an excitatory potential. On the other hand, if the cell is heavily injected with sulfate ions, which are also negatively charged, there is no such reversal. This simple test shows that under the influence of the inhibitory transmitter substance, which is still unidentified, the subsynaptic membrane becomes permeable momentarily to chloride ions but not to sulfate ions. During the generation of the IPSP the outflow of chloride ions is so rapid that it more than outweighs the flow of other ions that generate the normal inhibitory potential.
The effect of injecting motoneurons with more than 30 kinds of negatively lunged ions. With one exception the hydrated ions (ions bound to water) to which the cell membrane is permeable under the influence of the inhibitory transmitter substance are smaller than the hydrated ions to which the membrane is impermeable. The exception is the formate ion (HCO2-), which may have an ellipsoidal shape and so be able to pass through membrane pores that block smaller spherical ions.
Apart from the formate ion all the ions to which the membrane is permeable have a diameter not greater than 1.14 times the diameter of the potassium ion; That is, they are less than 2.9 angstrom units in diameter. Comparable investigations in other laboratories have found the same permeability effects, including the exceptional behavior of the formate ion, in fishes, toads and snails. It might be that the ionic mechanism responsible for synaptic inhibition is the same throughout the animal kingdom.
The significance of these and other studies is that they strongly suggest that the inhibitory transmitter substance open the membrane to the flow of potassium ions but not to sodium ions. It is known that the sodium ion is somewhat larger than any of the negatively charged ions, including the formate ion, that are able to pass through the membrane during synaptic inhibition. Testing the effectiveness of potassium ions by injecting excess amounts into the cell is not possible, however, because the excess is immediately diluted by an osmotic flow of water into the cell.
The concentration of potassium ions inside the nerve cell is about 30 times greater than the concentration outside, and to maintain this large difference in concentration without the help of some metabolic pumps inside of the membrane would have to be charged 90 millivolts negative with respect to the exterior. This implies that if the membrane were suddenly made porous to potassium ions, the resulting outflow of ions would make the inside potential of the membrane even more negative than it is in the resting state, and that is just what happens during synaptic inhibition. The membrane must not simultaneously become porous to sodium ions, because they exist in much higher concentration outside the cell than inside and their rapid inflow would more than compensate for the potassium outflow. In fact, the fundamental difference between synaptic excitation and synaptic inhibition is that the membrane freely passes sodium ions in response to the former and largely excludes the passage of sodium ions in response to the latter.
This fine discrimination between ions that are not very different in size must be explained by any hypothesis of synaptic action. It is most unlikely that the channels through the membrane are created afresh and accurately maintained for a thousandth of a second every time a burst of transmitter substance is released into the synaptic cleft. It is more likely that channels of at least two different sizes are built directly into the membrane structure. In some way the excitatory transmitter substance would selectively unplug the larger channels and permit the free inflow of sodium ions. Potassium ions would simultaneously flow out and thus would tend to counteract the large potential change that would be produced by the massive sodium inflow. The inhibitory transmitter substance would selectively unplug the smaller channels that are large enough to pass potassium and chloride ions but not sodium ions.
To explain certain types of inhibition other features must be added to this hypothesis of synaptic transmission. In the simple hypothesis chloride and potassium ions can flow freely through pores of all inhibitory synapses. It has been shown, however, that the inhibition of the contraction of heart muscle by the vagus nerve is due almost exclusively to potassium-ion flow. On the other hand, in the muscles of crustaceans and in nerve cells in the snail's brain synaptic inhibition is due largely to the flow of chloride ions. This selective permeability could be explained if there were fixed charges along the walls of the channels. If such charges were negative, they would repel negatively charged ions and prevent their passage; if they were positive, they would similarly prevent the passage of positively charged ions. One can now suggest that the channels opened by the excitatory transmitter are negatively charged and so do not permit the passage of the negatively charged chloride ion, even though it is small enough to move through the channel freely.
One might wonder if a given nerve cell can have excitatory synaptic action at some of its axon terminals and inhibitory action at others. The answer is no. Two different kinds of nerve cells are needed, one for each type of transmission and synaptic transmitter substance. This can readily be shown by the effect of strychnine and tetanus toxins in the spinal cord; They specifically prevent inhibitory synaptic action and leave excitatory action unaltered. As a result the synaptic excitation of nerve cells is uncontrolled and convulsions result. The special types of cells responsible for inhibitory synaptic action are now being recognized in many parts of the central nervous system.
This account of communication between nerve cells is necessarily oversimplified, yet it shows that some significant advances are being made at the level of individual components of the nervous system. By selecting the most favorable situations we have been able to throw light on some details of nerve-cell behavior. We can be encouraged by these limited successes. Nevertheless, the task of understanding in a comprehensive way how the human brain operates staggers its own imagination.
Our brain begins with its portion of the central nervous system contained within the skull. The brain is the control center for movement, sleep, hunger, thirst, and virtually every other vital activity necessary to survival. All human emotions - including love, hate, fear, anger, elation, and sadness - are controlled by the brain. It also receives and interprets the countless signals that are sent to it from other parts of the body and from the external environment. The brain makes us conscious, emotional, and intelligent.
The human brain has three major structural components: the large dome-shaped cerebrum, the smaller somewhat spherical cerebellum, and the brainstem. Prominent in the brainstem are the medulla oblongata and the thalamus - between the medulla and the cerebrum. The cerebrum is responsible for intelligence and reasoning. The cerebellum helps to maintain balance and posture. The medulla is involved in maintaining involuntary functions such as respiration, and the thalamus act as a relay center for electrical impulses traveling to and from the cerebral cortex.
The adult human brain is a 1.3-kg. (3-lb.) Mass of pinkish-gray jellylike tissue made up of approximately 100 billion nerve cells or neurons: The Neuroglia (supporting-tissue) cells, and vascular (blood-carrying) and other tissues.
Between the brain and the cranium - the part of the skull that directly covers the brain - are three protective membranes, or meninges. The outermost membrane, the dura mater, is the toughest and thickest. Below the dura mater is a middle membrane, called the arachnoid layer. The innermost membrane, the pia mater, consists mainly of small blood vessels and follows the contours of the surface of the brain.
A clear liquid, the cerebrospinal fluid, bathes the entire brain and fills a series of four cavities, called ventricles, near the center of the brain. The cerebrospinal fluid protects the internal portion of the brain from varying pressures and transports chemical substances within the nervous system.
From the outside, the brain appears as three associatively distinct but connected parts, the cerebrum (the Latin word for brain) - two large, almost symmetrical hemispheres; the cerebellum ('little brain') - two smaller hemispheres located at the back of the cerebrum; and the brain stem - a central core that gradually becomes the spinal cord, exiting the skull through an opening at its base called the foramen magnum. Two other major parts of the brain, the thalamus and the hypothalamus, lie in the midline above the brain stem underneath the cerebellum.
The brain and the spinal cord together make up the central nervous system, which communicates with the rest of the body through the peripheral nervous system. The peripheral nervous system consists of 12 pairs of cranial nerves extending from the cerebrum and brain stem; a system of other nerves branching throughout the body from the spinal cord, and the autonomic nervous system, which regulates vital functions is not very consciously of its own control, such as the activity of the heart muscle, smooth muscle (involuntary muscle found in the skin, blood vessels, and internal organs), and glands.
Many motor and sensory functions have been “mapped” to specific areas of the cerebral cortex, some of which are indicated here. In general, these areas exist in both hemispheres of the cerebrum, each serving the opposite side of the body. Fewer defined are the areas of association, located mainly in the frontal cortex, operatives in functions of thought and emotion and responsible for linking input from different senses. The areas of language are an exception: Both Wernicke’s area, concerned with the comprehension of spoken language, and Broca’s area, governing the production of speech, have been pinpointed on the cortex.
Most high-level brain functions take place in the cerebrum. Its two large hemispheres make up approximately 85 percent of the brain's weight. The exterior surface of the cerebrum, the cerebral cortex, is a convoluted, or folded, grayish layer of cell bodies known as the gray matter. The gray matter covers an underlying mass of fibers called the white matter. The convolutions are made up of ridgelike bulges, known as gyri, separated by small grooves called sulci and larger grooves called fissures. Approximately two-thirds of the cortical surface is hidden in the folds of the sulci. The extensive convolutions enable a very large surface area of brain cortices - roughly, 1.5 m2 (16 ft2) in an adult - to fit within the cranium. The pattern of these convolutions is similar, although not identical, in all humans.
The two cerebral hemispheres are partially separated from each other by a deep fold known as the longitudinal fissure. Communication between the two hemispheres is through several concentrated bundles of axons, called commissures, the largest of which is the corpus callosum.
Several major sulci divides the cortex into distinguishable regions. The central sulcus, or Rolandic fissure, runs from the middle of the top of each hemisphere downward, forwards, and toward another major sulcus, the lateral (side), or Sylvian, sulcus. These and other sulci and gyri divide the cerebrum into five lobes: The frontal, parietal, temporal, and occipital lobes and the insula.
Although the cerebrum is symmetrical in structure, with two lobes emerging from the brain stem and matching motor and sensory areas in each, certain intellectual functions are restricted to one hemisphere. A person’s dominant hemisphere is usually occupied with language and logical operations, while the other hemisphere controls emotion and artistic and spatial skills. In nearly all right-handed and many left-handed people, the left hemisphere is dominant.
The frontal lobe is the largest of the five and consists of all the cortices in front of the central sulcus. Broca's area, a part of the cortex related to speech, is located in the frontal lobe. The parietal lobe consists of the cortex behind the central sulcus to some sulcus near the back of the cerebrum known as the parieto-occipital sulcus. The parieto-occipital sulcus, in turn, forms the front border of the occipital lobe, which are the rearmost part of the cerebrum. The temporal lobe is to the side of and below the lateral sulcus. Wernicke's area, a part of the cortex related to the understanding of language, is located in the temporal lobe. The insula lies deep within the folds of the lateral sulcus.
The cerebrum receives information from all the sense organs and sends motor commands (signals that results in activity in the muscles or glands) to other parts of the brain and the rest of the body. Motor commands are transmitted by the motor cortex, a strip of cerebral cortex extending from side to side across the top of the cerebrum just in front of the central sulcus. The sensory cortex, parallel strips of cerebral cortex just in back of the central sulcus, receives input from the sense organs.
Many other areas of the cerebral cortex have also been mapped according to their specific functions, such as vision, hearing, speech, emotions, language, and other aspects of perceiving, thinking, and remembering. Cortical regions known as associative cortices are responsible for integrating multiple inputs, processing the information, and carrying out complex responses.
The cerebellum coordinates body movements. Located at the lower back of the brain beneath the occipital lobes, the cerebellum is divided into two lateral (side-by-side) lobes connected by a fingerlike bundle of white fibers called the vermis. The outer layer, or cortex, of the cerebellum consists of fine folds called folia. As in the cerebrum, the outer layer of cortical gray matter surrounds a deeper layer of white matter and nuclei (groups of nerve cells). Three fiber bundles called cerebellar peduncles connect the cerebellum to the three parts of the brain stem - the midbrain, the pons, and the medulla oblongata.
The cerebellum coordinates voluntary movements by fine-tuning commands from the motor cortex in the cerebrum. The cerebellum also maintains posture and balance by controlling muscle tone and sensing the position of the limbs. All motor activity, from hitting a baseball to fingering a violin, depends on the cerebellum.
The limbic system is a group of brain structures that play a role in emotion, memory, and motivation. For example, electrical stimulation of the amygdala in laboratory animals can provoke fear, anger, and aggression. The hypothalamus regulates hunger, thirst, sleep, body temperature, sexual drive, and other functions.
The thalamus and the hypothalamus lie underneath the cerebrum and connect it to the brain stem. The thalamus consist of two rounded masses of gray tissue lying within the middle of the brain, between the two cerebral hemispheres. The thalamus are the main relay station for incoming sensory signals to the cerebral cortex and for outgoing motor signals from it. All sensory input to the brain, except that of the sense of smell, connects to individual nuclei of the thalamus.
The hypothalamus lies beneath the thalamus on the midline at the base of the brain. It regulates or is involved directly in the control of many of the body's vital drives and activities, such as eating, drinking, temperature regulation, sleep, emotional behavior, and sexual activity. It also controls the function of internal body organs by means of the autonomic nervous system, interacts closely with the pituitary gland, and helps coordinate activities of the brain stem.
The brain stem, shown here in colored cross section, is the lowest part of the brain. It serves as the path for messages traveling between the upper brain and spinal cord but is also the seat of basic and vital functions such as breathing, blood pressure, and heart rates, as well as reflexes like eye movement and vomiting. The brain stem has three main parts: the medulla, pons, and midbrain. A canal runs longitudinally through these structures carrying cerebrospinal fluid. Also distributed along its length is a network of cells, referred to as the reticular formation, that governs the state of alertness.
The brain stem is revolutionarily the most primitive part of the brain and is responsible for sustaining the basic functions of life, such as breathing and blood pressure. It includes three main structures lying between and below the two cerebral hemispheres - the midbrain, pons, and medulla oblongata.
The topmost structure of the brain stem is the midbrain. It contains major relay stations for neurons transmitting signals to the cerebral cortex, as well as many reflex centers - pathways carrying sensory (input) information and motor (output) command. Relays and reflex centers for visual and auditory (hearing) functions are located in the top portion of the midbrain. A pair of nuclei called the superior colliculus control reflex actions of the eye, such as blinking, opening and closing the pupil, and focusing the lens. A second pair of nuclei, called the inferior colliculus, controls auditory reflexes, such as adjusting the ear to the volume of sound. At the bottom of the midbrain are reflex and relay centers relating to pain, temperature, and touch, as well as several regions associated with the control of movement, such as the red nucleus and the substantia nigra.
Continuous with and below the midbrain and directly in front of the cerebellum is a prominent bulge in the brain stem called the pons. The pons consists of large bundles of nerve fibers that connect the two halves of the cerebellum and also connect each side of the cerebellum with the opposite-side cerebral hemisphere. The pons serves mainly as a relay station linking the cerebral cortex and the medulla oblongata.
The long, stalklike lowermost portion of the brain stem is called the medulla oblongata. At the top, it is continuous with the pons and the midbrain; at the bottom, it makes a gradual transition into the spinal cord at the foramen magnum. Sensory and motor nerve fibers connecting the brain and the rest of the body cross over to the opposite side as they pass through the medulla. Thus, the left half of the brain communicates with the right half of the body, and the right half of the brain with the left half of the body.
Running up the brain stem from the medulla oblongata through the pons and the midbrain is a netlike formation of nuclei known as the reticular formation. The reticular formation controls respiration, cardiovascular function, digestion, levels of alertness, and patterns of sleep. It also determines which parts of the constant flow of sensory information into the body are received by the cerebrum.
There are two main types of brain cells, neurons and neuroglia. Neurons are responsible for the transmission and analysis of all electrochemical communication within the brain and other parts of the nervous system. Each neuron is composed of a cell body called a soma, and a major fiber called an axon, and a system of branches called dendrites. Axons, also called nerve fibers, convey electrical signals away from the soma and can be up to 1 m. (3.3 ft.) in length. Most axons are covered with a protective sheath of myelin, a substance made of fats and protein, which insulates the axon. Myelinated axons conduct neuronal signals faster than do unmyelinated axons. Dendrites convey electrical signals toward the soma, are shorter than axons, and are usually multiple and branching.
Neuroglial cells are twice as numerous as neurons and account for half of the brain's weight. Neuroglia (from glia, Greek for 'glue') provides structural support to the neurons. Neuroglial cells also form myelin, guide developing neurons, take up chemicals involved in cell-to-cell communication, and contribute to the maintenance of the environment around neurons.
Twelve pairs of cranial nerves arise symmetrically from the base of the brain and are numbered, from front to back, in the order in which they arise. They connect mainly with structures of the head and neck, such as the eyes, ears, nose, mouth, tongue, and throat. Some are motor nerves, controlling muscle movement; some are sensory nerves, conveying information from the sense organs; and others contain fibers for both sensory and motor impulses. The first and second pairs of cranial nerves - the olfactory (smell) nerves and the optic (vision) nerve - carry sensory information from the nose and eyes, respectively, to the undersurface of the cerebral hemispheres. The other ten pairs of cranial nerves originate in or end in the brain stem.
The brain functions by complex neuronal, or nerve cell, circuits. Communication between neurons is both electrical and chemical and always travels from the dendrites of a neuron, through its soma, and out its axon to the dendrites of another neuron.
Dendrites of one neuron receive signals from the axons of other neurons through chemicals known as neurotransmitters. The neurotransmitters set off electrical charges in the dendrites, which then carry the signals electrochemically to the soma. The soma integrates the information, which is then transmitted electrochemically down the axon to its tip.
At the tip of the axon, small, bubble-like structures called vesicles’ release neurotransmitters that carries the signal across the synapse, or gap, between two neurons. There are many types of neurotransmitters, including norepinephrine, dopamine, and serotonin. Neurotransmitters can be excitatory (that is, they excite an electrochemical response in the dendrite receptors) or inhibitory (they block the response of the dendrite receptors).
One neuron may communicate with thousands of other neurons, and many thousands of neurons are involved with even the simplest behavior. It is believed that these connections and their efficiency can be modified, or altered, by experience.
Scientists have used two primary approaches to studying how the brain works. One approach is to study brain function after parts of the brain have been damaged. Functions that disappear or that is no longer normal after injury to specific regions of the brain can often be associated with the damaged areas. The second approach is to study the response of the brain to direct stimulation or to stimulation of various sense organs.
Neurons are grouped by function into collections of cells called nuclei. These nuclei are connected to form sensory, motor, and other systems. Scientists can study the function of somatosensory (pain and touch), motor, olfactory, visual, auditory, language, and other systems by measuring the physiological (physical and chemical) change that occur in the brain when these senses are activated. For example, electroencephalography (EEG) measures the electrical activity of specific groups of neurons through electrodes attached to the surface of the skull. Electrodes incorporate directly into the brain can give readings of individual neurons. Changes in blood flow, glucose (sugar), or oxygen consumption in groups of active cells can also be mapped.
Although the brain appears symmetrical, how it functions is not. Each hemisphere is specializing and dominates the other in certain functions. Research has shown that hemispheric dominance is related to whether a person is predominantly right-handed or left-handed. In most right-handed people, the left hemisphere processes arithmetic, language, and speech. The right hemisphere interprets music, complex imagery, and spatial relationships and recognizes and expresses emotion. In left-handed people, the pattern of brain organization is more variable.
Hemispheric specialization has traditionally been studied in people who have sustained damage to the connections between the two hemispheres, as may occur with a stroke, an interruption of blood flow to an area of the brain that causes the death of nerve cells in that area. The division of functions between the two hemispheres has also been studied in people who have had to have the connection between the two hemispheres surgically cut in order to control severe epilepsy, a neurological disease characterized by convulsions and loss of consciousness.
The visual system of humans is one of the most advanced sensory systems in the body. More information is conveyed visually than by any other means. In addition to the structures of the eye itself, several cortical regions - collectively called a primary visual and visual associative cortex - as well as the midbrain are involved in the visual system. Conscious processing of visual input occurs in the primary visual cortex, but reflexive - that is, immediate and unconscious - responses occur at the superior colliculus in the midbrain. Associative cortical regions - specialized regions that can associate, or integrate, multiple inputs - in the parietal and frontal lobes along with parts of the temporal lobe are also involved in the processing of visual information and the establishment of visual memories.
Language involves specialized cortical regions in a complex interaction that allows the brain to comprehend and communicate abstract ideas. The motor cortex initiates impulses that travel through the brain stem to produce audible sounds. Neighboring regions of motor cortices, called the supplemental motor cortex, are involved in sequencing and coordinating sounds. Broca's area of the frontal lobe is responsible for the sequencing of language elements for output. The comprehension of language is dependent upon Wernicke's area of the temporal lobe. Other cortical circuits connect these areas.
Memory is usually considered a diffusely stored associative process - that is, it puts together information from many different sources. Although research has failed to identify specific sites in the brain as locations of individual memories, certain brain areas are critical for memory to function. Immediate recall - the ability to repeat short series of words or numbers immediately after hearing them - is thought to be located in the auditory associative cortex. Short-term memory - the ability to retain a limited amount of information for up to an hour - is located in the deep temporal lobe. Long-term memory probably involves exchanges between the medial temporal lobe, various cortical regions, and the midbrain.
The autonomic nervous system regulates the life support systems of the body reflexively - that is, without conscious direction. It automatically controls the muscles of the heart, digestive system, and lungs; Certain glands, and homeostasis - that is, the equilibrium of the internal environment of the body. The autonomic nervous system itself is controlled by nerve centers in the spinal cord and brain stem and is fine-tuned by regions higher in the brain, such as the midbrain and cortex. Reactions such as blushing indicate that cognitive, or thinking, centers of the brain are also involved in autonomic responses.
The brain is guarded by several highly developed protective mechanisms. The bony cranium, the surrounding meninges, and the cerebrospinal fluid all contribute to the mechanical protection of the brain. In addition, a filtration system called the blood-brain barrier protects the brain from exposure to potentially harmful substances carried in the bloodstream.
Brain disorders have a wide range of causes, including head injury, stroke, bacterial diseases, complex chemical imbalances, and changes associated with aging.
Head injury can initiate a cascade of damaging events. After a blow to the head, a person may be stunned or may become unconscious for a moment. This injury, called - concussion, - usually leaves no permanent damage. If the blow is more severe and hemorrhage (excessive bleeding) and swelling occurs, however, severe headache, dizziness, paralysis, a convulsion, or temporary blindness may result, depending on the area of the brain affected. Damage to the cerebrum can also result in profound personality changes.
Damage to Broca's area in the frontal lobe causes difficulty in speaking and writing, a problem known as Broca's aphasia. Injury to Wernicke's area in the left temporal lobe results in an inability to comprehend spoken language, called Wernicke's aphasia.
An injury or disturbance to a part of the hypothalamus may cause a variety of different symptoms, such as loss of appetite with an extreme drop in body weight, increase in appetite leading to obesity; Extraordinary thirst with excessive urination (diabetes insipidus), failure in body-temperature control, resulting in either low temperature (hypothermia) or high temperature (fever), excessive emotionality, and uncontrolled anger or aggression. If the relationship between the hypothalamus and the pituitary gland is damaged, other vital bodily functions may be disturbed, such as sexual function, metabolism, and cardiovascular activity.
Injury to the brain stem is even more serious because it houses the nerve centers that control breathing and heart action. Damage to the medulla oblongata usually results in immediate death.
A stroke is damage to the brain due to an interruption in blood flow. The interruption may be caused by a blood clot, constriction of a blood vessel, or rupture of a vessel accompanied by bleeding. A pouchlike expansion of the wall of a blood vessel, called an aneurysm, may weaken and burst, for example, because of high blood pressure.
Sufficient quantities of glucose and oxygen, transported through the bloodstream, are needed to keep nerve cells alive. When the blood supply to a small part of the brain is interrupted, the cells in that area die and the function of the area is lost. A massive stroke can cause a one-sided paralysis (hemiplegia) and sensory loss on the side of the body opposite the hemisphere damaged by the stroke.
Some brain diseases, such as multiple sclerosis and Parkinson disease, are progressive, becoming worse over time. Multiple sclerosis damages the myelin sheath around axons in the brain and spinal cord. As a result, the affected axons cannot transmit nerve impulses properly. Parkinson disease destroys the cells of the substantia nigra in the midbrain, resulting in a deficiency in the neurotransmitter dopamine that affects motor functions.
Cerebral palsy is a broad term for brain damage sustained close to birth that permanently affects motor function. The damage may take place either in the developing fetus, during birth, or just after birth and is the result of the faulty development or breaking down of motor pathways. Cerebral palsy is nonprogressive - that is, it does not worsen with time.
A bacterial infection in the cerebrum or in the coverings of the brain, swelling of the brain, or an abnormal growth of healthy brain tissue can all cause an increase in intracranial pressure and result in serious damage to the brain.
Scientists are finding that certain brain chemical imbalances are associated with mental disorders such as schizophrenia and depression. Such findings have changed scientific understanding of mental health and have resulted in new treatments that chemically correct these imbalances.
During childhood development, the brain is particularly susceptible to damage because of the rapid growth and reorganization of nerve connections. Problems that originate in the immature brain can appear as epilepsy or other brain-function problems in adulthood.
Several neurological problems are common in aging. Alzheimer's disease damages many areas of the brain, including the frontal, temporal, and parietal lobes. The brain tissue of people with Alzheimer's disease shows characteristic patterns of damaged neurons, known as plaques and tangles. Alzheimer's disease produces progressive dementia, characterized by symptoms such as failing attention and memory, loss of mathematical ability, irritability, and poor orientation in space and time.
A magnetic resonance imaging (MRI) scan of the human brain reveals the contours of one of the brain’s hemispheres. The gyri, or ridges, appear in red, while the sulci, or valleys, are shown in blue. Each person has slightly different patterns of gyri and sulci, which reflect individual differences in brain development.
Several commonly used diagnostic methods give images of the brain without invading the skull. Some portray anatomy - that is, the structure of the brain - whereas others measure brain function. Two or more methods may be used to complement each other, together providing a more complete picture than would be possible by one method alone.
Magnetic resonance imaging (MRI), introduced in the early 1980s, beams high-frequency radio waves into the brain in a highly magnetized field that causes the protons that form the nuclei of hydrogen atoms in the brain to reemit the radio waves. The reemitted radio waves are analyzed by computer to create thin cross-sectional images of the brain. MRI provides the most detailed images of the brain and is safer than imaging methods that use X-rays. However, MRI is a lengthy process and also cannot be used with people who have pacemakers or metal implants, both of which are adversely affected by the magnetic field.
Computed tomography (CT), also known as CT scans, developed in the early 1970s. This imaging method X-rays the brain from many different angles, feeding the information into a computer that produces a series of cross-sectional images. CT is particularly useful for diagnosing blood clots and brain tumors. It is a much quicker process than magnetic resonance imaging and is therefore advantageous in certain situations - for example, with people who are extremely ill.
This positron emission tomography (PET) scans of the brain shows the activity of brain cells in the resting state and during three types of auditory stimulation. PET uses radioactive substances introduced within the brain to measure such brain functions as cerebral metabolism, blood flow and volume, oxygen use, and the formation of neurotransmitters. This imaging method collects data from many different angles, feeding the information into a computer that produces a series of cross-sectional images.
Changes in brain function due to brain disorders can be visualized in several ways. Magnetic resonance spectroscopy measures the concentration of specific chemical compounds in the brain that may change during specific behaviors. Functional magnetic resonance imaging (fMRI) maps changes in oxygen concentration that correspond to nerve cell activity.
Positron emission tomography (PET), developed in the mid-1970s, uses computed tomography to visualize radioactive tracers, radioactive substances are introduced into the brain intravenously or by inhalation. PET can measure such brain functions as cerebral metabolism, blood flow and volume, oxygen use, and the formation of neurotransmitters. Single photon emission computed tomography (SPECT), developed in the 1950s and 1960s, used radioactive tracers to visualize the circulation and volume of blood in the brain.
Brain-imaging studies have provided new insights into sensory, motor, language, and memory processes, as well as brain disorders such as epilepsy, cerebrovascular disease; Alzheimer's, Parkinson, and Huntington's diseases, and various mental disorders, such as schizophrenia.
Although all vertebrate brains share the same basic three-part structure, the development of their constituent parts varies across the evolutionary scale. In fish, the cerebrum is dwarfed by the rest of the brain and serves mostly to process input from the senses. In reptiles and amphibians, the cerebrum is proportionally larger and begins to connect and form conclusions about this input. Birds have well-developed optic lobes, making the cerebrum even larger. Among mammals, the cerebrum dominates the brain. It is most developed among primates, in whom cognitive ability is the highest.
In lower vertebrates, such as fish and reptiles, the brain is often tubular and bears a striking resemblance to the early embryonic stages of the brains of more highly evolved animals. In all vertebrates, the brain is divided into three regions: the forebrain (prosencephalon), the midbrain (mesencephalon), and the hindbrain (rhombencephalon). These three regions further sub-divide into different structures, systems, nuclei, and layers.
The more highly evolved the animal, the more complex is the brain structure. Human beings have the most complex brains of all animals. Evolutionary forces have also resulted in a progressive increase in the size of the brain. In vertebrates lower than mammals, the brain is small. In meat-eating animals, particularly primates, the brain increases dramatically in size.
The cerebrum and cerebellum of higher mammals are highly convoluted in order to fit the most gray matter surface within the confines of the cranium. Such highly convoluted brains are called gyrencephalic. Many lower mammals have a smooth, or lissencephalic (smooth head), cortical surfaces.
There is also evidence of evolutionary adaption of the brain. For example, many birds depend on an advanced visual system to identify food at great distances while in flight. Consequently, their optic lobes and cerebellum are well developed, giving them keen sight and outstanding motor coordination in flight. Rodents, on the other hand, as nocturnal animals, do not have a well-developed visual system. Instead, they rely more heavily on other sensory systems, such as a highly-developed sense of smell and facial whiskers.
Recent research in brain function suggests that there may be sexual differences in both brain anatomy and brain function. One study indicated that men and women may use their brains differently while thinking. Researchers used functional magnetic resonance imaging to observe which parts of the brain were activated as groups of men and women tried to determine whether sets of nonsense words rhymed. Men used only Broca's area in this task, whereas women used Broca's area plus an area on the right side of the brain.
The Cell, in [biology] is the most basic unit of life. Cells are the smallest structures capable of basic life processes, such as taking in nutrients, expelling waste, and reproducing. All living things are composed of cells. Some microscopic organisms, such as bacteria and protozoa, are unicellular, meaning they consist of a single cell. Plants, animals, and fungi are multicellular; that is, they are composed of a great many cells working in concert. But whether it makes up an entire bacterium or is just one of the trillions in a human being, the cell is a marvel of design and efficiency. Cells carry out thousands of biochemical reactions each minute and reproduce new cells that perpetuate life.
The word cell refers to several types of organisms. Cells such as paramecia, dinoflagellates, diatoms, and spirochetes are self-maintaining organisms; cells such as lymphocytes, erythrocytes, muscle cells, nerve cells, cardiac muscle, and chromoplasts are more specializing cells that are a part of higher multicellular organisms. Nonetheless, of its size or whether the cell is a complete organism or just part of an organism, all cells have certain structural components in common. All cells have some type of outer cell boundary that permits some materials to leave and enter the cell and a cell interior composed of a water-rich, fluid material called cytoplasm that contains hereditary material in the form of deoxyribonucleic acid (DNA).
Cells vary considerably in size. The smallest cell, a type of bacterium known as a mycoplasma, measures 0.0001 mm. (0.000004 in.) in diameter; 10,000 mycoplasmas in a row are only as wide as the diameter of a human hair. Among the largest cells are the nerve cells that run down a giraffe’s neck; these cells can exceed 3 m. (9.7 ft.) in length. Human cells also display a variety of sizes, from small red blood cells that measure 0.00076 mm. (0.00003 in.) to liver cells that may be ten times larger. About 10,000 average-sized human cells can fit on the head of a pin.
Along with their differences in size, cells present an array of shapes. Some, such as the bacterium Escherichia coli, resemble rods. The paramecium, a type of protozoan, is a slipper shaped. The amoeba, another protozoan, has an irregular form that changes shape as it moves around. Plant cells typically resemble boxes or cubes. In humans, the outermost layers of skin cells are flat, while muscle cells are long and thin. Some nerve cells, with their elongated, tentacle-like extensions, suggest an octopus.
In multicellular organisms, shape is typically tailored to the cell’s job. For example, flat skin cells pack tightly into a layer that protects the underlying tissues from invasions by bacteria. Long, thin muscle cells’ contract readily to move bones. The numerous extensions from a nerve cell enable it to connect to several other nerve cells in order to send and receive messages rapidly and efficiently.
By itself, each cell is a model of independence and self-containment. Like some miniature, walled city in perpetual rush hour, the cell constantly bustles with traffic, shuttling essential molecules from place to place to carry out the business of living. Despite their individuality, however, cells also display a remarkable ability to join, communicate, and coordinate with other cells. The human body, for example, consists of an estimated 20 to 30 trillion cells. Dozens of different kinds of cells are organized into specialized groups called tissues. Tendons and bones, for example, are composed of connective tissue, whereas skin and mucous membranes are built from epithelial tissue. Different tissue types are assembled into organs, which are structures specialized to perform particular functions. Examples of organs include the heart, stomach, and brain. Organs, in turn, are organized into systems such as the circulatory, digestive, or nervous systems. All together, these assembled organ systems form the human body.
The components of cells are molecules, nonliving structures formed by the union of atoms. Small molecules serve as building blocks for larger molecules. Proteins, nucleic acids, carbohydrates, and lipids, which include fats and oils, are the four major molecules that underlie cell structure and also participate in cell functions. For example, a tightly organized arrangement of lipids, proteins, and protein-sugar compounds forms the plasma membrane, or outer boundary, of certain cells. The organelles, membrane-bound compartments in cells, are built largely from proteins. Biochemical reactions in cells are guided by enzymes, specialized proteins that speed up chemical reactions. The nucleic acid deoxyribonucleic acid (DNA) contains the hereditary information for cells, and another nucleic acid, ribonucleic acid (RNA), works with DNA to build the thousands of proteins the cell needs.
Cells fall into one of two categories: Prokaryotic or eukaryotic, in a prokaryotic cell, found only in bacteria and archaebacteria, all the components, including the DNA, mingle freely in the cell’s interior, a single compartment. Eukaryotic cells, which make up plants, animals, fungi, and all other life forms, contain numerous compartments, or organelles, within each cell. The DNA in eukaryotic cells is enclosed in a special organelle called the nucleus, which serves as the cell’s command center and information library. The term prokaryote comes from Greek words that mean “before the nucleus” or “prenucleus,” while eukaryote means “a true nucleus.”
Bacteria’s cells typically are surrounded by a rigid, protective cell wall. The cell membrane, also called the plasma membrane, regulates passage of materials into and out of the cytoplasm, the semi-fluid that fill the cell. The DNA, located in the nucleoid region, contains the genetic information for the cell. Ribosomes carry out protein synthesis. Many bacteria contain some pilus (plural pili), a structure that extends out of the cell to transfer DNA to another bacterium. The flagellum, found in numerous species, is used for the locomotion. Some bacteria contain a plasmid, a small chromosomes with extra genes. Others have a capsule, a sticky substance external to the cell wall that protects bacteria from attack by white blood cells. Mesosomes were formerly thought to be structures with unknown functions, but now are known to be artifacts created when cells are prepared for viewing with electron microscopes.
Prokaryotic cells are among the tiniest of all cells, ranging in size from 0.0001 to 0.003 mm. (0.000004 to 0.0001 in.) in diameter. About a hundred typical prokaryotic cells lined up in a row would match the thickness of a book page. These cells, which can be rod-like, spherical, or spiral in shape, are surrounded by a protective cell wall. Like most cells, prokaryotic cells live in a watery environment, whether it is soil moisture, a pond, or the fluid surrounding cells in the human body. Tiny pores in the cell wall enable water and the substances dissolved in it, such as oxygen, to flow into the cell; these pores also allow wastes to flow out.
Pushed up against the inner surface of the prokaryotic cell wall is a thin membrane called the plasma membrane. The plasma membrane, composed of two layers of flexible lipid molecules and interspersed with durable proteins, is both supple and strong. Unlike the cell wall, whose open pores allow the unregulated traffic of materials in and out of the cell, the plasma membrane is selectively permeable, meaning it allows only certain substances to pass through. Thus, the plasma membrane actively separates the cell’s contents from its surrounding fluids.
While small molecules such as water, oxygen, and carbon dioxide diffuse freely across the plasma membrane, the passage of many larger molecules, including amino acids (the building blocks’ of proteins) and sugars, is carefully regulated. Specialized transport proteins accomplish this task. The transport proteins span the plasma membrane, forming an intricate system of pumps and channels through which traffic is conducted. Some substances swirling in the fluid around the cell can enter it only if they bind to and are escorted in by specific transport proteins. In this way, the cell fine-tunes its internal environment.
The plasma membrane encloses the cytoplasm, the semifluid that fill the cell. Composed of about 65 percent water, the cytoplasm is packed with up to a billion molecules per cell, a rich storehouse that includes enzymes and dissolved nutrients, such as sugars and amino acids. The water provides a favorable environment for the thousands of biochemical reactions that take place in the cell.
Within the cytoplasm of all prokaryote is deoxyribonucleic acid (DNA), a complex molecule in the form of a double helix, a shape similar to a spiral staircase. The DNA is about 1,000 times the length of the cell, and to fit inside, it repeatedly twists and folds to form a compact structure called a chromosome. The chromosome in prokaryote is circular, and is located in a region of the cell called the nucleoid. Often, smaller chromosomes called plasmids are located in the cytoplasm. The DNA is divided into units called genes, just like a long train is divided into separate cars. Depending on the species, the DNA contains several hundred or even thousands of genes. Typically, one gene contains coded instructions for building all or part of a single protein. Enzymes, which are specialized proteins, determine virtually all the biochemical reactions that support and sustain the cell.
Also, immersed in the cytoplasm are the only organelles in prokaryotic cells. Tiny bead-like structures called ribosomes. These are the cell’s protein factories. Following the instructions encoded in the DNA, ribosomes churn out proteins by the hundreds every minute, providing needed enzymes, the replacements for worn-out transport proteins, or other proteins required by the cell.
While relatively simple in construction, prokaryotic cells display extremely complex activity. They have a greater range of biochemical reactions than those found in their larger relatives, the eukaryotic cells. The extraordinary biochemical diversity of prokaryotic cells is manifested in the wide-ranging lifestyles of the archaebacteria and the bacteria, whose habitats include polar ice, deserts, and hydrothermal vents - deep regions of the ocean under great pressure where hot water geysers erupt from cracks in the ocean floor.
An animal cell typically contains several types of membrane-bound organs, or organelles. The nucleus directs activities of the cell and carries genetic information from generation to generation. The mitochondria generates energy for the cell. Proteins are manufactured by ribosomes, which are bound to the rough endoplasmic reticulum or float free in the cytoplasm. The Golgi apparatus modifies, packages, and distributes proteins while lysosomes store enzymes for digesting food. The entire cell is wrapped in a lipid membrane that selectively permits materials to pass in and out of the cytoplasm.
Eukaryotic cells are typically about ten times larger than prokaryotic cells. In animal cells, the plasma membrane, rather than a cell wall, forms the cell’s outer boundary. With a design similar to the plasma membrane of prokaryotic cells, it separates the cell from its surroundings and regulates the traffic across the membrane.
The eukaryotic cell cytoplasm is similar to that of the prokaryote cell except for one major difference: Eukaryotic cells house a nucleus and numerous other membrane-enclosed organelles. Like separate rooms of a house, these organelles enable specialized functions to be carried out efficiently. The building of proteins and lipids, for example, takes place in separate organelles where specialized enzymes geared for each job are located.
The plasma membrane that surrounds eukaryotic cells is a dynamic structure composed of two layers of phospholipid molecules interspersed with cholesterol and proteins. Phospholipids are composed of a hydrophilic, or water-loving, head and two tails, which are hydrophobic, or water-hating. The two phospholipid layers face each other in the membrane, with the heads directed outward and the tails pointing inward. The water-attracting heads anchor the membrane to the cytoplasm, the watery fluid inside the cell, and also to the water surrounding the cell. The water-hating tails block large water-soluble molecules from passing through the membrane while permitting fat-soluble molecules, including medications such as tranquilizers and sleeping pills, to freely cross the membrane. Proteins embedded in the plasma membrane carry out a variety of functions, including transport of large water soluble molecules such as sugars and certain amino acids. Glycoproteins, proteins bonded to carbohydrates, serve in part to identify the cell as belonging to a unique organism, enabling the immune system to detect foreign cells, such as invading bacteria, which carry different glycoproteins. Cholesterol molecules in the plasma membrane act as stabilizers that limit the movement of the two slippery phospholipids layer, which slide back and forth in the membrane. Tiny gaps in the membrane enable small molecules such as oxygen to diffuse readily into and out of the cell. Since cells constantly use up oxygen, decreasing its concentration within the cell, the higher concentration of oxygen outside the cell causes a net flow of oxygen into the cell. The steady stream of oxygen into the cell enables it to carry out aerobic respiration continually, a process that provides the cell with the energy needed to carry out its functions.
The nucleus is the largest organelle in an animal cell. It contains numerous strands of DNA, the length of each strand being many times the diameter of the cell. Unlike the circular prokaryotic DNA, long sectors of eukaryotic DNA pack into the nucleus by wrapping around proteins. As a cell begins to divide, each DNA strand folds over onto itself several times, forming a rod-shaped chromosome.
The nucleus is surrounded by a double-layered membrane that protects the DNA from potentially damaging chemical reactions that occur in the cytoplasm. Messages pass between the cytoplasm and the nucleus through nuclear pores, which are holes in the membrane of the nucleus. In each nuclear pore, molecular signals flash back and forth as often as ten times per second. For example, a signal to activate a specific gene comes into the nucleus and instructions for production of the necessary protein go out to the cytoplasm.
The nucleus, present in eukaryotic cells, is a discrete structure containing chromosomes, which hold the genetic information for the cell. Separated from the cytoplasm of the cell by a double-layered membrane called the nuclear envelope, and the nucleus contains a cellular material called nucleoplasm. Nuclear pores, present around the circumference of the nuclear membrane, allow the exchange of cellular materials between the nucleoplasm and the cytoplasm.
Attached to the nuclear membrane is an elongated membranous sac called the endoplasmic reticulum. This organelle tunnels through the cytoplasm, folding back and forth on itself to form a series of membranous stacks. Endoplasmic reticulums take two forms: Rough and smooth. A rough endoplasmic reticulum (RER) is so called because it appears bumpy under a microscope. The bumps are actually thousands of ribosomes attached to the membrane’s surface. The ribosomes in eukaryotic cells have the same function as those in prokaryotic cells - protein synthesis - but they differ slightly in structure. Eukaryote ribosomes bound to the endoplasmic reticulum help assemble proteins that typically are exported from the cell. The ribosomes work with other molecules to link amino acids to partially completed proteins. These incomplete proteins then travel to the inner chamber of the endoplasmic reticulum, where chemical modifications, such as the addition of a sugar, are carried out. Chemical modifications of lipids are also carried out in the endoplasmic reticulum.
The endoplasmic reticulum and its bound ribosomes are particularly dense in cells that produce many proteins for export, such as the white blood cells of the immune system, which produce and secrete antibodies. Some ribosomes that manufacture proteins are not attached to the endoplasmic reticulum. These so-called free ribosomes are dispersed in the cytoplasm and typically make proteins - many of them enzymes - that remain in the cell.
The second form of an endoplasmic reticulum, the smooth endoplasmic reticulum (SER), lacks ribosomes and has an even surface. Within the winding channels of the smooth endoplasmic reticulum are the enzymes needed for the construction of molecules such as carbohydrates and lipids. The smooth endoplasmic reticulum is prominent in liver cells, where it also serves to detoxify substances such as alcohol, drugs, and other poisons.
Proteins are transported from free and bound ribosomes to the Golgi apparatus, an organelle that resembles a stack of deflated balloons. It is packed with enzymes that complete the processing of proteins. These enzymes add sulfur or phosphorus atoms to certain regions of the protein, for example, or chop off tiny pieces from the ends of the proteins. The completed protein then leaves the Golgi apparatus for its final destination inside or outside the cell. During its assembly on the ribosome, each protein has acquired a group of from 4 to 100 amino acids called a signal. The signal works as a molecular shipping label to direct the protein to its proper location.
Lysosomes are small, often spherical organelles that function as the cell’s recycling center and garbage disposal. Powerful digestive enzymes concentrated in the lysosome break down worn-out organelles and ship their building blocks to the cytoplasm where they are used to construct new organelles. Lysosomes also dismantle and recycle proteins, lipids, and other molecules.
The mitochondria is the powerhouse of the cell. Within these long, slender organelles, which can appear oval or bean shaped under the electron microscope, enzymes convert the sugar glucose and other nutrients into adenosine triphosphate (ATP). This molecule, in turn, serves as an energy battery for countless cellular processes, including the shuttling of substances across the plasma membrane, the building and transport of proteins and lipids, the recycling of molecules and organelles, and the dividing of cells. Muscle and liver cells are particularly active and require dozens and sometimes up to hundreds mitochondria per cell to meet their energy needs. Mitochondria is unusual in that they contain their own DNA in the form of a prokaryote-like circular chromosome; Have their own ribosomes, which resemble prokaryotic ribosomes, and divide independently of the cell.
Unlike the tiny prokaryotic cell, the relatively large eukaryotic cell requires structural support. The cytoskeleton, a dynamic network of protein tubes, filaments, and fibers, crisscrosses the cytoplasm, anchoring the organelles in place and providing shape and structure to the cell. Many components of the cytoskeleton are assembled and disassembled by the cell as needed. During cell division, for example, a special structure called a spindle is built to move chromosomes around. After cell division, the spindle, no longer needed, is dismantled. Some components of the cytoskeleton serve as microscopic tracks along which proteins and other molecules travel like miniature trains. Recent research suggests that the cytoskeleton also may be a mechanical communication structure that converses with the nucleus to help organize events in the cell.
Plant cells have all the components of animal cells and boast several added features, including chromoplasts, a central vacuole, and a cell wall. Chromoplasts convert light energy - typically from the Sun - into the sugar glucose, a form of chemical energy, in a process known as photosynthesis. Chromoplasts, like mitochondria, possess a circular chromosome and prokaryote-like ribosomes, which manufacture the proteins that the chloroplasts typically need.
The central vacuole of a mature plant cell typically takes up most of the room in the cell. The vacuole, a membranous bag, crowds the cytoplasm and organelles to the edges of the cell. The central vacuole stores water, salts, sugars, proteins, and other nutrients. In addition, it stores the blue, red, and purple pigments that give certain flowers their colors. The central vacuole also contains plant wastes that taste bitter to certain insects, thus discouraging the insects from feasting on the plant.
In plant cells, a sturdy cell wall surrounds and protects the plasma membrane. Its pores enable materials to pass freely into and out of the cell. The strength of the wall also enables a cell to absorb water into the central vacuole and swell without bursting. The resulting pressure in the cells provides plants with rigidity and support for stems, leaves, and flowers. Without sufficient water pressure, the cells collapse and the plant wilts.
To stay alive, cells must be able to carry out a variety of functions. Some cells must be able to move, and most cells must be able to divide. All cells must maintain the right concentration of chemicals in their cytoplasm, ingest food and use it for energy, recycle molecules, expel wastes, and construct proteins. Cells must also be able to respond to changes in their environment.
Although many forms of bacteria are not capable of independent movement, species such as the Salmonella bacterium pictured here can move by means of fine threadlike projections called flagella. The arrangement of flagella across the surface of the bacterium differs from species to species; they can be present at the ends of the bacterium or all across the body surface. Forward movement is accomplished either by a tumbling motion or in a forward manner without tumbling.
Many unicellular organisms swim, glide, thrash, or crawl to search for food and escape enemies. Swimming organisms often move by means of a flagellum, a long tail-like structure made of protein. Many bacteria, for example, have one, two, or many flagella that rotate like propellers to drive the organism along. Some single-celled eukaryotic organisms, such as the euglena, also have a flagellum, but it is longer and thicker than the prokaryotic flagellum. The eukaryotic flagellums work by waving up and down like a whip. In higher animals, the sperm cell uses a flagellum to swim toward the female egg for fertilization.
Movement in eukaryotes is also accomplished with cilia, short, hairlike proteins built by centrioles, which are barrel-shaped structures located in the cytoplasm that assemble and break down protein filaments. Typically, thousands of cilia extend through the plasma membrane and cover the surface of the cell, giving it a dense, hairy appearance. By beating its cilia as if they were oars, an organism such as the paramecium propels itself through its watery environment. In cells that do not move, cilia are used for other purposes. In the respiratory tract of humans, for example, millions of ciliated cells prevent inhaled dust, smog, and microorganisms from entering the lungs by sweeping them up on a current of mucus into the throat, where they are swallowed. Eukaryotic flagella and cilia are formed from basal bodies, small protein structures located just inside the plasma membrane. Basal bodies also help to anchor flagella and cilia.
Still other eukaryotic cells, such as amoebas and white blood cells, move by amoeboid motion, or crawling. They extrude their cytoplasm to form temporary pseudopodia, or false feet, which actually are placed in front of the cell, rather like extended arms. They then drag the trailing end of their cytoplasm up to the pseudopodia. A cell using amoeboid motion would lose a race to a euglena or paramecium. But while it is slow, amoeboid motion is strong enough to move cells against a current, enabling water-dwelling organisms to pursue and devour prey, for example, or white blood cells roaming the blood stream to stalk and engulf a bacterium or virus.
An amoeba, a single-celled organism lacking internal organs, is shown approaching a much smaller paramecium, which it begins to engulf with large outflowings of its cytoplasm, called pseudopodia. Once the paramecium is completely engulfed, a primitive digestive cavity, called a vacuole, forms around it. In the vacuole, acids break the paramecium down into chemicals that the amoeba can diffuse back into its cytoplasm for nourishment.
All cells require nutrients for energy, and they display a variety of methods for ingesting them. Simple nutrients dissolved in pond water, for example, can be carried through the plasma membrane of pond-dwelling organisms via a series of molecular pumps. In humans, the cavity of the small intestine contains the nutrients from digested food, and cells that form the walls of the intestine use similar pumps to pull amino acids and other nutrients from the cavity into the bloodstream. Certain unicellular organisms, such as amoebas, are also capable of reaching out and grabbing food. They used a process known as endocytosis, in which the plasma membrane surrounds and engulfed the food particle, enclosing it in a sac, called a vesicle, that is within the amoeba’s interior.
Cells require energy for a variety of functions, including moving, building up and breaking down molecules, and transporting substances across the plasma membrane. Nutrients contain energy, but cells must convert the energy locked in nutrients to another form - specifically, the ATP molecule, the cell’s energy battery - before it is useful. In single-celled eukaryotic organisms, such as the paramecium, and in multicellular eukaryotic organisms, such as plants, animals, and fungi, mitochondria is responsible for this task. The interior of each mitochondrion consists of an inner membrane that is folded into a mazelike arrangement of separate compartments called cristae. Within the cristae, enzymes form an assembly line where the energy in glucose and other energy-rich nutrients is harnessed to build ATP; thousands of ATP molecules are constructed each second in a typical cell. In most eukaryotic cells, this process requires oxygen and is known as aerobic respiration.
Some prokaryotic organisms also carry out aerobic respiration. They lack mitochondria, however, and carry out aerobic respiration in the cytoplasm with the help of enzymes sequestered there. Many prokaryote species live in environments where there is little or no oxygen, environments such as mud, stagnant ponds, or within the intestines of animals. Some of these organisms produce ATP without oxygen in a process known as anaerobic respiration, where sulfur or other substances take the place of oxygen. Still other prokaryotes, and yeast, a single-celled eukaryote, build ATP without oxygen in a process known as fermentation.
Almost all organisms rely on the sugar glucose to produce ATP. Glucose is made by the process of photosynthesis, in which light energy is transformed to the chemical energy of glucose. Animals and fungi cannot carry out photosynthesis and depend on plants and other photosynthetic organisms for this task. In plants, as we have seen, photosynthesis takes place in organelles called chloroplasts. Chloroplasts contain numerous internal compartments called thylakoids where enzymes aid in the energy conversion process. A single leaf cell contains 40 to 50 chloroplasts. With sufficient sunlight, one large tree is capable of producing upwards of two tons of sugar in a single day. Photosynthesis in prokaryotic organisms - typically aquatic bacteria - is carried out with enzymes clustered in plasma membrane folds called chromatophores. Aquatic bacteria produce the food consumed by tiny organisms living in ponds, rivers, lakes, and seas.
bosomes
A typical cell must have on hand, about. 30,000 proteins at any-one time. Many of these proteins are enzymes needed to construct the major molecules used by cells - carbohydrates, lipids, proteins, and nucleic acids - nor to aid in the breakdown of such molecules after they have worn out. Other proteins are part of the cell’s structure - the plasma membrane and ribosomes, for example. In animals, proteins also function as hormones and antibodies, and they function like delivery trucks to transport other molecules around the body. Hemoglobin, for example, is a protein that transports oxygen in red blood cells. The cell’s demand for proteins never ceases.
Before a protein can be made, however, the molecular directions to build, it must be extracted from one or more genes. In humans, for example, one gene holds the information for the protein insulin, the hormone that cells need to import glucose from the bloodstream, while at least two genes hold the information for collagen, the protein that imparts strength to skin, tendons, and ligaments. The process of building proteins begins when enzymes, in response to a signal from the cell, bind to the gene that carries the code for the required protein, or part of the protein. The enzymes transfer the code to a new molecule called messenger RNA, which carries the code from the nucleus to the cytoplasm. This enables the original genetic code to remain safe in the nucleus, with messenger RNA delivering small bits and pieces of information from the DNA to the cytoplasm as needed. Depending on the cell type, hundreds or even thousands of molecules of messenger RNA are produced each minute.
Once in the cytoplasm, the messenger RNA molecule links up with a ribosome. The ribosome moves along the messenger RNA like a monorail car along a track, stimulating another form of RNA - transfer RNA - to gather and link the necessary amino acids, pooled in the cytoplasm, to form the specific protein, or section of protein. The protein is modified as necessary by the endoplasmic reticulum and Golgi apparatus before embarking on its mission. Cells teem with activity as they forge the numerous, diverse proteins that are indispensable for life. For a more detailed discussion about protein synthesis, When there are a hundred or more cells, they formed a hollow ball of cells, called a blastula, surrounding a fluid-filled cavity. Later divisions produce three layers of cells - endoderm (inner), mesoderm (middle), and ectoderm (outer) - from which the principal features of the animal will differentiate.
Most cells divide at some time during their life cycle, and some divide dozens of times before they die. Organisms rely on cell division for reproduction, growth, and repair and replacement of damaged or worn out cells. Three types of cell division occur: Binary fission, mitosis, and meiosis. Binary fission, the method used by prokaryotes, produces two identical cells from one cell. The more complex process of mitosis, which also produces two genetically identical cells from a single cell, is used by many unicellular eukaryotic organisms for reproduction. Multicellular organisms use mitosis for growth, cell repair, and cell replacement. In the human body, for example, an estimated 25 million mitotic cell divisions occur every second in order to replace cells that have completed their normal life cycles. Cells of the liver, intestine, and skin may be replaced every few days. Recent research indicates that even brain cell, once thought to be incapable of mitosis, undergo cell division in the part of the brain associated with memory.
In a landmark intersection of science and fiction, cloning leapt from the world’s imagination to its front page in February 1997. It arrived in the innocent form of a sheep named Dolly: The first exact genetic duplicate of an adult mammal due to genetic engineering. Scottish scientists had created Dolly from deoxyribonucleic acid (DNA) - the basic unit of heredity - taken from a single adult sheep cell. The accomplishment threw open the door to profoundly ethical as well as scientific controversy over the potential uses and abuses of cloning. “However the debate is resolved,” wrote Los Angeles Times science reporter Thomas H. Maugh II, “the genie is irretrievably out of the bottle.”
The type of cell division required for sexual reproduction is meiosis. Sexually reproducing organisms include seaweeds, fungi, plants, and animals - including, of course, human beings. Meiosis differs from mitosis in that cell division begins with a cell that has a full complement of chromosomes and ends with gamete cells, such as sperm and eggs, that have only half the complement of chromosomes. When a sperm and egg unite during fertilization, the cell resulting from the union, called a zygote, contains the full number of chromosomes.
The story of how cells evolved remains an open and actively investigated question in science. The combined expertise of physicists, geologists, chemists, and evolutionary biologists has been required to shed light on the evolution of cells from the nonliving matter of early Earth. The planet formed about 4.5 billion years ago, and for millions of years, violent volcanic eruptions blasted substances such as carbon dioxide, nitrogen, water, and other small molecules into the air. These small molecules, bombarded by ultraviolet radiation and lightning from intense storms, collided to form the stable chemical bonds of larger molecules, such as amino acids and nucleotides - the building blocks of proteins and nucleic acids. Experiments indicate that these larger molecules form spontaneously under laboratory conditions that simulate the probable early environment of Earth.
Scientists speculate that rain may have carried these molecules into lakes to create a primordial soup - the breeding ground for the assembly of proteins, the nucleic acid RNA, and lipids. Some scientists postulate that these more complex molecules formed in hydrothermal vents rather than in lakes. Other scientists propose that these key substances may have reached Earth on meteorites from outer space. Regardless of the origin or environment, however, scientists do agree that proteins, nucleic acids, and lipids provided the raw materials for the first cells. In the laboratory, scientists have observed lipid molecules joining to form spheres that resemble a cell’s plasma membrane. As a result of these observations, scientists postulate that millions of years of molecular collisions resulted in lipid spheres enclosing RNA, the simplest molecule capable of self-replication. These primitive aggregations would have been the ancestors of the first prokaryotic cells.
Fossil studies indicate that Cyanobacteria, bacteria capable of photosynthesis, were among the earliest bacteria to evolve, an estimated 3.4 billion to 3.5 billion years ago. In the environment of the early Earth, there were no oxygen, and cyanobacteria probably used fermentation to produce ATP. Over the eons, cyanobacteria performed photosynthesis, which produces oxygen as a byproduct; The result was the gradual accumulation of oxygen in the atmosphere. The presence of oxygen set the stage for the evolution of bacteria that used oxygen in aerobic respiration, a more efficient ATP-producing process than fermentation. Some molecular studies of the evolution of genes in archaebacteria suggest that these organisms may have evolved in the hot waters of hydrothermal vents or hot springs slightly earlier than cyanobacteria, around 3.5 billion years ago. Like cyanobacteria, archaebacteria probably relied on fermentation to synthesize ATP.
Eukaryotic cells may have evolved from primitive prokaryotes about 2 billion years ago. One hypothesis suggests that some prokaryotic cells lost their cell walls, permitting the cell’s plasma membrane to expand and fold. These folds, ultimately, may have given rise to separate compartments within the cell - the forerunners of the nucleus and other organelles now found in eukaryotic cells. Another key hypothesis is known as endosymbiosis. Molecular studies of the bacteria-like DNA and ribosomes in mitochondria and chloroplasts indicate that mitochondrion and chloroplast ancestors were once free-living bacteria. Scientists propose that these free-living bacteria were engulfed and maintained by other prokaryotic cells for their ability to produce ATP efficiently and to provide a steady supply of glucose. Over generations, eukaryotic cells situated with mitochondria - the ancestors of animals - or with both mitochondria and chloroplasts - the ancestors of plants - evolved.
The first observations of cells were made in 1665 by English scientist Robert Hooke, who used a crude microscope of his own invention to examine a variety of objects, including a thin piece of cork. Noting the rows of tiny boxes that made up the dead wood’s tissue, Hooke coined the term cell because the boxes reminded him of the small cells occupied by monks in a monastery. While Hooke was the first to observe and describe cells, he did not comprehend their significance. At about the same time, the Dutch maker of microscopes Antoni van Leeuwenhoek pioneered the invention of one of the best microscopes of the time. Using his invention, Leeuwenhoek was the first to observe, draw, and describe a variety of living organisms, including bacteria gliding in saliva, one-celled organisms cavorting in pond water, and sperm swimming in semen. Two centuries passed, however, before scientists grasped the true importance of cells.
Many advances have been made in microscope technology. This article from the 1994 Collier’s Year Book begins with the microscope most young students are familiar with and tracks the breakthroughs in the development of new types of microscopes - including those that use ultrasonic imaging and those that “feel” an object’s surface.
Modern ideas about cells appeared in the 1800s, when improved light microscopes enabled scientists to observe more details of cells. Working together, German botanist Matthias Jakob Schleiden and German zoologist Theodor Schwann recognized the fundamental similarities between plant and animal cells. In 1839 they proposed the revolutionary idea that all living things are made up of cells. Their theory gave rise to modern biology: a whole new way of seeing and investigating the natural world.
By the late 1800s, as light microscopes improved still further, scientists were able to observe chromosomes within the cell. Their research was aided by new techniques for staining parts of the cell, which made possible the first detailed observations of cell division, including observations of the differences between mitosis and meiosis in the 1880s. In the first few decades of the 20th century, many scientists focused on the behavior of chromosomes during cell division. At that time, it was generally held that mitochondria transmitted the hereditary information. By 1920, however, scientists determined that chromosomes carry genes and that genes transmit hereditary information from generation to generation.
During this period, scientists began to understand some of the chemical processes in cells. In the 1920s, the ultracentrifuge was developed. The ultracentrifuge is an instrument that spins cells or other substances in test tubes at high speeds, which causes the heavier parts of the substance to fall to the bottom of the test tube. This instrument enabled scientists to separate the relatively abundant and heavy mitochondria from the rest of the cell and study their chemical reactions. By the late 1940s, scientists were able to explain the role of mitochondria in the cell. Using refined techniques with the ultracentrifuge, scientists subsequently isolated the smaller organelles and gained an understanding of their functions.
The deoxyribonucleic acid (DNA) molecule is the genetic blueprint for each cell and ultimately the blueprint that determines every characteristic of a living organism. In 1953 American biochemist James Watson, left, and British biophysicist Francis Crick, right, described the structure of the DNA molecule as a double helix, somewhat like a spiral staircase with many individual steps. Their work was aided by X-ray diffraction pictures of the DNA molecule taken by British biophysicist Maurice Wilkins and British physical chemist Rosalind Franklin. In 1962 Crick, Watson, and Wilkins received the Nobel Prize for their pioneering work on the structure of the DNA molecule.
While some scientists were studying the functions of cells, others were examining details of their structure. They were aided by a crucial technological development in the 1940s, the invention of the electron microscope, which uses high-energy electrons instead of light waves to view specimens. New generations of electron microscopes have provided resolution, or the differentiation of separate objects, thousands of times more powerful than that available in light microscopes. This powerful resolution revealed organelles such as the endoplasmic reticulum, lysosomes, the Golgi apparatus, and the cytoskeleton. The scientific fields of cell structure and function continue to complement each other as scientists explore the enormous complexity of cells.
The discovery of the structure of DNA in 1953 by American biochemist James D. Watson and British biophysicist Francis Crick ushered in the era of molecular biology. Today, investigation inside the world of cells - of genes and proteins at the molecular level - constitutes one of the largest and fastest moving areas in all of science. One particularly active field in recent years has been the investigation of cell signaling, the process by which molecular messages find their way into the cell via a series of complex protein pathways in the cell.
Another busy area in cell biology concerns programmed cell death, or apoptosis. Millions of times per second in the human body, cells commit suicide as an essential part of the normal cycle of cellular replacement. This also seems to be a check against disease: When mutations build up within a cell, the cell will usually self-destruct. If this fails to occur, the cell may divide and give rise to mutated daughter cells, which continue to divide and spread, gradually forming a growth called a tumor. This unregulated growth by rogue cells can be benign, or harmless, or cancerous, which may threaten healthy tissue. The study of apoptosis is one avenue that scientists explore in an effort to understand how cells become cancerous.
Scientists are also discovering exciting aspects of the physical forces within cells. Cells employ a form of architecture called tensegrity, which enables them to withstand battering by a variety of mechanical stresses, such as the pressure of blood flowing around cells or the movement of organelles within the cell. Tensegrity stabilizes cells by evenly distributing mechanical stresses to the cytoskeleton and other cell components. Tensegrity also may explain how a change in the cytoskeleton, where certain enzymes are anchored, initiates biochemical reactions within the cell, and can even influence the action of genes. The mechanical rules of tensegrity may also account for the assembly of molecules into the first cells. Such new insights - made some 300 years after the tiny universe of cells was first glimpsed - show that cells continue to yield fascinating new worlds of discovery.
The Nervous System signifies of those elements within the animal organism that are concerned with the reception of stimuli, the transmission of nerve impulses, or the activation of muscle mechanisms.
The reception of stimuli is the function of special sensory cells. The conducting elements of the nervous system are cells called neurons; these may be capable of only slow and generalized activity, or they may be highly efficient and rapidly conducting units. The specific response of the neuron—the nerve impulse - and the capacities of the cell to be stimulated make this cell a receiving and transmitting unit capable of transferring information from one part of the body to another.
Each nerve cell consists of a central portion containing the nucleus, known as the cell body, and one or more structures referred to as axons and dendrites. The dendrites are rather short extensions of the cell body and are involved in the reception of stimuli. The axon, by contrast, is usually a single elongated extension, it is especially important in the transmission of nerve impulses from the region of the cell body to other cells.
Although all many-celled animals have some kind of nervous system, the complexity of its organization varies considerably among different animal types. In simple animals such as jellyfish, the nerve cells form a network capable of mediating only a relatively stereotyped response. In more complex animals, such as shellfish, insects, and spiders, the nervous system is more complicated. The cell bodies of neurons are organized in clusters called ganglia. These clusters are interconnected by the neuronal processes to form a ganglionated chain. Such chains are found in all vertebrates, in which they represent a special part of the nervous system, related especially to the regulation of the activities of the heart, the glands, and the involuntary Vertebrate animals have a bony spine and skull in which the central part of the nervous system is housed; The peripheral part extends throughout the remainder of the body. That part of the nervous system located in the skull is referred to as the brain that found in the spine is called the spinal cord. The brain and the spinal cord are continuous through an opening in the base of the skull; Both are also in contact with other parts of the body through the nerves. The distinction made between the central nervous system and the peripheral nervous system is based on the different locations of the two intimately related parts of a single system. Some of the processes of the cell bodies conduct sense impressions and others conduct muscle responses, called reflexes, such as those caused by pain.
In the skin are cells of several types called receptors; each is especially sensitive to particular stimuli. Free nerve endings are sensitive to pain and are directly activated. The neurons so activated send impulses into the central nervous system and have junctions with other cells that have axons extending back into the periphery. Impulses are carried from processes of these cells to motor endings within the muscles. These neuromuscular endings excite the muscles, resulting in muscular contraction and appropriate movement. The pathway taken by the nerve impulse in mediating this simple response is in the form of a two-neuron arc that begins and ends in the periphery. Many of the actions of the nervous system can be explained on the basis of such reflex arcs, which are chains of interconnected nerve cells, stimulated at one end and capable of bringing about movement or glandular secretion at the other.
The cranial nerves connect to the brain by passing through openings in the skull, or cranium. Nerves associated with the spinal cord pass through openings in the vertebral column and are called spinal nerves. Both cranial and spinal nerves consist of large numbers of processes that convey impulses to the central nervous system and also carry messages outward; the former processes are called afferent, and the latter are called efferent. Afferent impulses are referred to as sensory; efferent impulses are referred to as either somatic or visceral motor, according to what part of the body they reach. Most nerves are mixed nerves made up of both sensory and motor elements.
The cranial and spinal nerves are paired; The number in humans are 12 and 31, respectively. Cranial nerves are distributed to the head and neck regions of the body, with one conspicuous exception: the tenth cranial nerve, called the vagus. In addition to supplying structures in the neck, the vagus is distributed to structures located in the chest and abdomen. Vision, auditory and vestibular sensation, and taste is mediated by the second, eighth, and seventh cranial nerves, respectively. Cranial nerves also mediate motor functions of the head, the eyes, the face, the tongue, and the larynx, as well as the muscles that function in chewing and swallowing. Spinal nerves, after they exit from the vertebrae, are distributed in a band-like fashion to regions of the trunk and to the limbs. They interconnect extensively, thereby forming the brachial plexus, which runs to the upper extremities, and the lumbar plexus, which passes to the lower limbs.
Among the motor’s fibers may be found groups that carry impulses to viscera. These fibers are designated by the special name of autonomic nervous system. That system consists of two divisions, more or less antagonistic in function, that emerge from the central nervous system at different points of origin. One division, the sympathetic, arises from the middle portion of the spinal cord, joins the sympathetic ganglionated chain, courses through the spinal nerves, and is widely distributed throughout the body. The other division, the parasympathetic, arises both above and below the sympathetic, that is, from the brain and from the lower part of the spinal cord. These two divisions control the functions of the respiratory, circulatory, digestive, and urogenital systems.
Consideration of disorders of the nervous system is the province of neurology; Psychiatry deals with behavioral disturbances of a functional nature. The division between these two medical specialties cannot be sharply defined, because neurological disorders often manifest both organic and mental symptoms.
Diseases of the nervous system include genetic malformations, poisonings, metabolic defects, vascular disorders, inflammations, degeneration, and tumors, and they involve either nerve cells or their supporting elements. Vascular disorders, such as cerebral hemorrhage or other forms of a stroke, are among the most common causes of paralysis and other neurologic complications. Some diseases exhibit peculiar geographic and age distribution. In temperate zones, multiple sclerosis is a common degenerative disease of the nervous system, but it is rare in the Tropics.
The nervous system is subject to infection by a great variety of bacteria, parasites, and viruses. For example, meningitis, or infection of the meninges investing the brain and spinal cord, can be caused by many different agents. On the other hand, one specific virus causes rabies. Some viruses causing neurological ills effect only certain parts of the nervous system. For example, the virus causing poliomyelitis commonly affects the spinal cord, as Viruses manufacturing encephalitis attack the brain.
Inflammations of the nervous system are named according to the part affected. Myelitis is an inflammation of the spinal cord; Neuritis is an inflammation of a nerve. It may be caused not only by infection but also by poisoning, alcoholism, or injury. Tumors originating in the nervous system usually are composed of meningeal tissue or neuroglia (supporting tissue) cells, depending on the specific part of the nervous system affected, but other types of a tumor may metastasize to or invade the nervous system. In certain disorders of the nervous system, such as neuralgia, migraine, and epilepsy, no evidence may exist of organic damage. Another disorder, cerebral palsy, is associated with birth defects.
Pain, is an unpleasant sensory or emotional experience caused by real or potential injury or damage to the body or described in terms of such damage. Scientists believe that pain evolved in the animal kingdom as a valuable three-part warning system. First, it warns of injury. Second, pain protects against further injury by causing a reflexive withdrawal from the source of injury. Finally, pain leads to a period of reduced activity, enabling injuries to heal more efficiently.
Pain is difficult to measure in humans because it has an emotional, or psychological component as well as a physical component. Some people express extreme discomfort from relatively small injuries, while others show little or no pain even after suffering severe injury. Sometimes pain is present even though no injury is apparent at all, or pain lingers long after an injury appears to have healed.
The signals that warn the body of tissue damage are transmitted through the nervous system. In this system, the basic unit is the nerve cell or neuron. A nerve cell is composed of three parts: a central cell body, a single major branching fiber called an axon, and a series of smaller branching fibers known as dendrites. Each nerve cell meets other nerve cells at certain points on the axons and dendrites, forming a dense network of interconnected nerve fibers that transmit sensory information about touch, pressure, or warmth, as well as pain.
Sensory information is transmitted from the different parts of the body to the brain via the spinal cord, which is a complex set of nerves that extend from the brain down along the back, protected by the bones of the spine. About as wide as a finger, the spinal cord is like a cable packed with many bundles of wires. The bundles are nerve pathways for transmitting information. But the spinal cord is more than just a message transmitter, it is also an extension of the brain. It contains neurons that process incoming sensory information, and generates messages to be sent back down to cells in other parts of the body.
In the nervous system, a message-carrying impulse travels from one end of a nerve cell to the other by means of an electrical impulse. When it reaches the terminal end of a nerve cell, the impulse trigger’s tiny sacs called presynaptic vessicles to release their contents, chemical messengers called neurotransmitters. The neurotransmitters float across the synapse, or gap between adjacent nerve cells. When they reach the neighboring nerve cell, the neurotransmitters fit into specialized receptor sites much as a key fits into a lock, causing that nerve cell to “fire,” or generate an electric message-carrying impulse. As the message continues through the nervous system, the presynaptic cell absorbs the excess neurotransmitters, and repackages them in presynaptic versicles in a process called neurotransmitter reuptake.
Information being transmitted between and within the brain and spinal cord travels through the nervous system using both chemical and electrical mechanisms. A message-carrying impulse travels from one end of a nerve cell to another by means of an electric signal. When the electric signal reaches the terminal end of a nerve cell, a gap called a synapse prevents the electric signal from crossing to the next cell. The electric signal triggers the cell to release chemicals called neurotransmitters, which float across the synapse to the neighboring nerve cell. These neurotransmitters fit into specialized receptors found on the adjacent nerve cell, much as a key fits into a lock, generating an electric impulse in the neighboring cell. This new impulse travels to the end of the long cell, in turn triggering the release of neurotransmitters to carry the message across the next synapse. Not all neurotransmitters initiate a message in a neighboring nerve cell. Some specialize in preventing neighboring cells from generating an electrical signal, while others function as helpers, facilitating the message's journey to the brain.
While most of the sensory nerves in the skin and other body tissues have special structures covering their nerve endings, those nerves that signal injury have free nerve endings. These simple nerve endings specialize in detecting noxious stimuli - a catchall term for injury-causing stimuli such as intense heat, extreme pressure, or sharp pricks or cuts. The nerve endings that detect pain are called nociceptors, and the process of transmitting pain signals when harmful stimulation occurs is called nociception. Several million nociceptors are interlaced through the tissues and organs of the body.
When a person experiences an injury, such as a stubbed toe, specialized cells called nociceptors sense potential tissue damage (1) and send an electric signal, called an impulse, to the spinal cord via a sensory nerve (2). A specialized region of the spinal cord known as the dorsal horn (3) processes the pain signal, immediately sending another impulse back down the leg via a motor nerve (4). This causes the muscles in the leg to contract and pull the toe away from the source of injury (6). At the same time, the dorsal horn sends another impulse up the spinal cord to the brain. During this trip, the impulse travels between nerve cells. When the impulse reaches a nerve ending (7), the nerve released chemical messengers, called neurotransmitters, which carry the message to the adjacent nerve. When the impulse reaches the brain (8), it is analyzed and processed as an unpleasant physical and emotional sensation.
An injury triggers pain signals in two types of nociceptors, one with large, insulated axons known as A-delta fibers and one with small, uninsulated axons known as C fibers. The large A-delta fibers conduct signals quickly, and the smaller C fibers transmit information slowly. The difference in the functions of these two fibers becomes obvious to a person who stubs a toe. At first the injured person is aware of a sharp, flashing pain at the point of injury. Generated by the A-delta fibers, this short-lived pain intrudes upon the thoughts and perceptions occurring in the brain. Just as this first pain subsides, a second pain begins that is vague, throbbing, and persistent. This sensation is derived from the C fibers.
Pain information from the A-delta and C fibers travels through the spinal cord to the brain. When it receives the pain message, the spinal cord generates impulses that travel back down to muscles, which lead to a reflexive contraction that pulls the body away from the source of injury. Other reflexes may affect skin temperature, blood flow, sweating, and other changes.
While this reflex action is underway, the pain message continues up the spinal cord to relay centers in the brain. The sensory information is routed to many other parts of the brain, including the cortex, where thinking processes occur
The Adrenal Gland is the vital endocrine gland that secretes hormones into the bloodstream, situated, in humans, on top of the upper end of each kidney. The two parts of the gland - the inner portion, or medulla, and the outer portion, or the cortex - are like separate organs: They are composed of different types of tissue and perform different functions. The adrenal medulla, composed of chromaffin cells secretes the hormone epinephrine, also called adrenaline, in response to stimulation of the sympathetic nervous system at times of stress. The medulla also secretes the hormone norepinephrine, which plays a role in maintaining normal blood circulation. The hormones of the medulla are called catecholamines. Unlike the adrenal cortex, the medulla can be removed without endangering the life of an individual.
The adrenal outer layer, or cortex, secretes about 30 steroid hormones, but only a few are secreted in significant amounts. Aldosterone, one of the most important hormones, regulates the balance of salt and water in the body. Cortisone and hydrocortisone are necessary to regulate fat, carbohydrate, and protein metabolism. Adrenal sex steroids have a minor influence on the reproductive system. Modified steroids, now produced synthetically, are superior to naturally secreted steroids for treatment of Addison's disease and other disorders.
Adrenocorticotropic Hormone is also known as corticotropin, hormones secreted by the anterior part of the pituitary gland. The specific function of ACTH is to stimulate the growth and secretions of the cortex (outer layers) of the adrenal gland. One of these secretions is cortisone, a hormone involved in carbohydrate and protein metabolisms. ACTH is used medically for its anti-inflammatory action to alleviate symptoms of allergies and arthritis. ACTH is a complex protein molecule containing 39 amino acids. Its molecular weight is approximately 5000. The biological activity of the ACTH of various animal species is similar to that of humans, but the sequence of amino acids has been found to vary somewhat among species. ACTH production is controlled in part by the hypothalamus and in part by the existing levels of adrenal gland hormones. ACTH levels increased in response to stress, disease, and decreased blood pressure.
The Pituitary Gland is the master endocrine gland in vertebrate animals. The hormones secreted by the pituitary stimulate and control the functioning of almost all the other endocrine glands in the body. Pituitary hormones also promote growth and control the water balance of the body.
The pituitary is a small bean-shaped, reddish-gray organ located in the saddle-shaped depression (sella turcica) in the floor of the skull (the sphenoid bone) and attached to the base of the brain by a stalk; it is located near the hypothalamus. The pituitary has two lobes - the anterior lobe, or adenohypophysis, and the posterior lobe, or neurohypophysis - which differ in structure and function. The anterior lobe is derived embryologically from the roof of the pharynx and is composed of groups of epithelial cells separated by blood channels; the posterior lobe is derived from the base of the brain and is composed of nervous connective tissue and nerve-like secreting cells. The area between the anterior and posterior lobes of the pituitary is called the intermediate lobe; it has the same embryological origin as the anterior lobe.
Concentrated chemical substances, or hormones, which control 10 to 12 functions in the body, have been obtained as extracts from the anterior pituitary glands of cattle, sheep, and swine. Eight hormones have been isolated, purified, and identified; All of them are peptides, that is, they are composed of amino acids. A growth hormone (GH), or the somatotropic hormone (STH), is essential for normal skeletal growth and is neutralized during adolescence by the gonadal sex hormones. Thyroid-stimulating hormones (TSH) control the normal functioning of the thyroid gland, and the adrenocorticotropic hormone (ACTH) controls the activity of the cortex of the adrenal glands and takes part in the stress reaction. Prolactin, also called lactogenic, luteotropic, or mammotropic hormone, initiates milk secretion in the mammary gland after the mammary tissues have been prepared during pregnancy by the secretion of other pituitary and sex hormones. The two gonadotropic hormones are follicle-stimulating hormones (FSH) and a luteinizing hormone (LH). Follicle-stimulating hormones stimulates the formation of the Graafian follicle in the female ovary and the development of spermatozoa in the male. The luteinizing hormone stimulates the formation of ovarian hormones after ovulation and initiates lactation in the female, in the male, it stimulates the tissues of the testes to elaborate testosterone. In 1975 scientists identified the pituitary peptide endorphin, which acts in experimental animals as a natural pain reliever in times of stress. Endorphin and ACTH are made as parts of a single large protein, which subsequently splits. This may be the body's mechanism for coordinating the physiological activities of two stress-induced hormones. The same large prohormone that contains ACTH and endorphin also contains short peptides called melanocyte-stimulating hormones. These substances are analogous to the hormone that regulates pigmentation in fish and amphibians, but in humans they have no known function.
Research has shown that the hormonal activity of the anterior lobe is controlled by chemical messengers sent from the hypothalamus through tiny blood vessels to the anterior lobe. In the 1950s, the British neurologist Geoffrey Harris discovered that cutting the blood supply from the hypothalamus to the pituitary impaired the function of the pituitary. In 1964, chemical agents called releasing factors were found in the hypothalamus; These substances, it was learned, affect the secretion of growth hormones, a thyroid-stimulating hormone called thyrotropin, and the gonadotropic hormones involving the testes and ovaries. In 1969 the American endocrinologist Roger Guillemin and colleagues isolated and characterized thyrotropin-releasing factors, which stimulates the secretion of thyroid-stimulating hormones from the pituitary. In the next few years his group and that of the American physiologist Andrew Victor Schally isolated the luteinizing hormone-releasing factor, which stimulates secretion of both LH and FSH, and somatostatin, which inhibits release of growth hormones. For this work, which proved that the brain and the endocrine system are linked, they shared the Nobel Prize in physiology or medicine in 1977. Human somatostatin was one of the first substances to be grown in bacteria by recombinant DNA.
The presence of the releasing factors in the hypothalamus helped to explain the action of the female sex hormones, estrogen and progesterone, and their synthetic versions contained in oral contraceptives, or birth-control pills. During a woman's normal monthly cycle, several hormonal changes are needed for the ovary to produce an egg cell for possible fertilization. When the estrogen level in the body declines, the follicle-releasing factor (FRF) flows to the pituitary and stimulates the secretion of the follicle-stimulating hormone. Through a similar feedback principle, the declining level of progesterone causes a release of luteal-releasing factors (LRF), which stimulates secretion of the luteinizing hormone. The ripening follicle in the ovary then produces estrogen, and the high level of that hormone influences the hypothalamus to shut down temporarily the production of FSH. Increased progesterone feedback to the hypothalamus shuts down LH production by the pituitary. The daily doses of synthetic estrogen and progesterone in oral contraceptives, or injections of the actual hormones, inhibit the normal reproductive activity of the ovaries by mimicking the effect of these hormones on the hypothalamus.
In lower vertebrates this part of the pituitary secretes melanocyte-stimulating hormones, which brings about skin-color changes. In humans, it is present only for a short time early in life and during pregnancy, and is not known to have any function.
Two hormones are secreted by the posterior lobe. One of these is the antidiuretic hormone (ADH), vasopressin. Vasopressin stimulates the kidney tubules to absorb water from the filtered plasma that passes through the kidneys and thus controls the amount of urine secreted by the kidneys. The other posterior pituitary hormone is oxytocin, which causes the contraction of the smooth muscles in the uterus, intestines, and blood arterioles. Oxytocin stimulates the contractions of the uterine muscles during the final stage of pregnancy to stimulate the expulsion of the fetus, and it also stimulates the ejection, or let-down, of milk from the mammary gland following pregnancy. Synthesized in 1953, oxytocin was the first pituitary hormone to be produced artificially. Vasopressin was synthesized in 1956.
Pituitary functioning may be disturbed by such conditions as tumors, blood poisoning, blood clots, and certain infectious diseases. Conditions resulting from a decrease in anterior-lobe secretion include dwarfism, acromicria, Simmonds's disease, and Fröhlich's syndrome. The dwarfism occurs when anterior pituitary deficiencies occur during childhood; acromicria, in which the bones of the extremities are small and delicate, results when the deficiency occurs after puberty. Simmonds's disease, which is caused by extensive damage to the anterior pituitary, is characterized by premature aging, loss of hair and teeth, anemia, and emaciation; it can be fatal. Fröhlich's syndrome, also called adiposogenital dystrophy, is caused by both anterior pituitary deficiency and a lesion of the posterior lobe or hypothalamus. The result is obesity, dwarfism, and retarded sexual development. Glands under the influence of anterior pituitary hormones are also affected by anterior pituitary deficiency.
Over secretion of one of the anterior pituitary hormones, somatotropin, results in a progressive chronic disease called acromegaly, which is characterized by enlargement of some parts of the body. Posterior-lobe deficiency results in diabetes insipidus.
Tissue
Tissue, - group of associated, similarly structured cells that perform specialized functions for the survival of the organism. Animal tissues, to which this article is limited, take their first form when the blastula cells, arising from the fertilized ovum, differentiate into three germ layers: the ectoderm, mesoderm, and endoderm. Through further cell differentiation, or histogenesis, groups of cells grow into more specialized units to form organs made up, usually, of several tissues of similarly performing cells. Animal tissues are classified into four main groups.
These tissues include the skin and the inner surfaces of the body, such as those of the lungs, stomach, intestines, and blood vessels. Because its primary function is to protect the body from injury and infection, epitheliums are made up of tightly packed cells with little intercellular substance between them.
About 12 kinds of epithelial tissue occur. One kind is stratified squamous tissue found in the skin and the linings of the esophagus and vagina. It is made up of thin layers of flat, scalelike cells that form rapidly above the blood capillaries and is pushed toward the tissue surface, where they die and are shed. Another is a simple columnar epithelium, which lines the digestive system from the stomach to the anus; Simple columnar epithelium cells stand upright and not only control the absorption of nutrients but also secrete mucus through individual goblet cells. Glands are formed by the inward growth of epithelium-for examples, the sweat glands of the skin and the gastric glands of the stomach. Outward growth results in hair, nails, and other structures.
These tissues, which support and hold parts of the body together, comprises the fibrous and elastic connective tissues, the adipose (fatty) tissues, and cartilage and bone. In contrast to an epithelium, the cells of these tissues are widely separated from one another, with a large amount of intercellular substance between them. The cells of fibrous tissue, found throughout the body, connect to one another by an irregular network of strands, forming a soft, cushiony layer that also supports blood vessels, nerves, and other organs. Adipose tissue has a similar function, except that its fibroblasts also contain store fat. Elastic tissue, found in ligaments, the trachea, and the arterial walls, stretches and contracts again with each pulse beat. In the human embryo, the fibroblast cells that originally secreted collagen for the formation of fibrous tissue later change to secrete a different form of protein called chondrion, for the formation of cartilage, some cartilage later becomes calcified by the action of osteoblast to form bones. Blood and lymph are also often considered connective tissues.
Tissues, which contract and relax, comprise the striated, smooth, and cardiac muscles. Striated muscles, also called skeletal or voluntary muscles, include those that are activated by the somatic, or voluntary, nervous system. They are joined together without cell walls and have several nuclei. The smooth, or involuntary muscles, which are activated by the autonomic nervous system, are found in the internal organs and consist of simple sheets of cells. Cardiac muscles, which have characteristics of both striated and smooth muscles, are joined together in a vast network. These highly complex groups of cells, called ganglia, transfer information from one part of the body to another. Each neuron, or nerve cell, consists of a cell body with branching dendrites and one long fiber, or axons. The dendrites connect one neuron to another; The axon transmits impulses to an organ or collects impulses from a sensory organ.
Crossing a Synapse
In the nervous system, a message-carrying impulse travels from one end of a nerve cell to the other by means of an electrical impulse. When it reaches the terminal end of a nerve cell, the impulse trigger’s tiny sacs called presynaptic vessicles to release their contents, chemical messengers called neurotransmitters. The neurotransmitters float across the synapse, or gap between adjacent nerve cells. When they reach the neighboring nerve cell, the neurotransmitters fit into specialized receptor sites much as a key fits into a lock, causing that nerve cell to fire or generate an electric message-carrying impulse. As the message continues through the nervous system, the presynaptic cell absorbs the excess neurotransmitters, and repackages them in presynaptic versicles in a process called neurotransmitter reuptake.
Reflex
Reflex, in physiology, is the involuntary response to a stimulus by the animal organism. In its simplest form, it consisted of the stimulation of an afferent nerve through a sense organ, or receptor, followed by transmission of the stimulus, usually through a nerve center, to an efferent motor nerve, resulting in action of a muscle or gland, called the effector. In most reflex action, however, the stimulus passes through one or more intermediate nerve cells, which modify and direct its action, sometimes to the extent of involving the muscular activity of the entire organism. For example, a painful stimulus applied to the hand causes a reflex withdrawal of the hand, which involves contraction of the flexor group of muscles and reflexation of the opposing extensor group; if the stimulus is strong, the coordinating nerve cells pass it to the arm muscles and also to the muscles of the trunk and legs, the result being a jump that removes not only the arm, but the entire person from the vicinity of the painful stimulus.
The system of coordinating nerve cells is such that several different kinds of stimuli may produce the same result. For example, the stimulus produced by the sight of food and that caused by the smell of food travel different afferent pathways, but both have a common final path that stimulates the salivary glands to secretion. The final common path may also be activated through associated nerve tracts by a stimulus that ordinarily is not directly connected with the response. This type of reflex was named conditioned reflex by its discoverer, the Russian physiologist Ivan Pavlov, about 1904. Pavlov found that sounding a bell every time a dog was about to be given food eventually caused a reflex flow of saliva, which later persisted even when no food was produced. Elaborations of this habituative type of reflex are regarded by some physiologists and psychologists as an important basis for many behaviors, both voluntary and involuntary.
The normal pathways of many reflexes are generally known, and the presence, absence, or exaggerations of the normal physical responses to certain stimuli are symptoms used by neurologists to determine the condition of the neural pathways involved. A familiar reflex commonly tested by physicians is the patellar reflex, in which an involuntary jerk of the knee is evoked by lightly striking the tendon of the patella, or kneecap, indicating the efficiency of certain nerve tracts in the spinal cord.
Like all other cells, neurons contain charged ions: Potassium and sodium (positively charged) and chlorine (negatively charged). Neurons differ from other cells in that they are able to produce a nerve impulse. A neuron is polarized - that is, it has an overall negative charge inside the cell membrane because of the high concentration of chlorine ions and low concentration of potassium and sodium ions. The concentration of these same ions is exactly reversed outside the cell. This charge differential represents stored electrical energy, sometimes referred to as membrane potential or resting potential. The negative charge inside the cell is maintained by two features. The first is the selective permeability of the cell membrane, which is more permeable to potassium than sodium. The second feature is sodium pumps within the cell membrane that actively pump sodium out of the cell. When depolarization occurs, this charge differential across the membrane is reversed, and a nerve impulse is produced.
Depolarization is a rapid change in the permeability of the cell membrane. When sensory input or any other kind of stimulating current is received by the neuron, the membrane permeability is changed, allowing a sudden influx of sodium ions into the cell. The high concentration of sodium, or action potential, changes the overall charges within the cell from negative to positive. The local changes in ion concentration triggers similar reactions along the membrane, propagating the nerve impulse. After a brief period called the refractory period, during which the ionic concentration returned to resting potential, the neuron can repeat this process.
Nerve impulses travel at different speeds, depending on the cellular composition of a neuron. Where speed of impulse is important, as in the nervous system, axons are insulated with a membranous substance called myelin. The insulation provided by myelin maintains the ionic charge over long distances. Nerve impulses are propagated at specific points along the myelin sheath; These points are called the nodes of Ranvier. Examples of myelinated axons are those in sensory nerve fibers and nerves connected to skeletal muscles. In non-myelinated cells, the nerve impulse is propagated more diffusely.
The nervous system has two divisions: The somatic, which allow voluntary control over skeletal muscle, and the autonomic, which is involuntary and controls cardiac and smooth muscle and glands. The autonomic nervous system has two divisions: The sympathetic and the parasympathetic. Many, but not all, of the muscles and glands that distribute nerve impulses to the larger interior organs possess a double nerve supply; in such cases the two divisions may exert opposing effects. Thus, the sympathetic system increases heartbeat, and the parasympathetic system decreases heartbeat. The two nervous systems are not always antagonistic, however. For example, both nerve supplies to the salivary glands excite the cells of secretion. Furthermore, a single division of the autonomic nervous system may both excite and inhibit a single effector, as in the sympathetic supply to the blood vessels of skeletal muscle. Finally, the sweat glands, the muscles that cause involuntary erection or bristling of the hair, the smooth muscle of the spleen, and the blood vessels of the skin and skeletal muscle are actuated only by the sympathetic division.
Voluntary movement of head, limbs, and body is caused by nerve impulses arising in the motor area of the cortex of the brain and carried by cranial nerves or by nerves that emerge from the spinal cord to connect with skeletal muscles. The reaction involves both excitation of nerve cells stimulating the muscles involved and inhibition of the cells that stimulate opposing muscles. A nerve impulse is an electrical change within a nerve cell or fiber; Measured in millivolts, it lasts a few milliseconds and can be recorded by electrodes.
The human brain has three major structural components: The large dome-shaped cerebrum, the smaller somewhat spherical cerebellum, and the brainstem. Prominent in the brainstem is the medulla oblongata (the egg-shaped enlargement at the center) and the thalamus (between the medulla and the cerebrum). The cerebrum is responsible for intelligence and reasoning. The cerebellum helps to maintain balance and posture. The medulla is involved in maintaining involuntary functions such as respiration, and the thalamus act as a relay center for electrical impulses traveling to and from the cerebral cortex. Lack of blood flow to any part of the brain results in a stroke, permanent damage that interferes with the functions of the affected part of the brain.
Movement may occur also in direct response to an outside stimulus, thus, a tap on the knee causes a jerk, and a light shone into the eye makes the pupil contract. These involuntary responses are called reflexes. Various nerve terminals called receptors constantly send impulses into the central nervous system. These are of three classes: exteroceptors, which are sensitive to pain, temperature, touch, and pressure; interoceptors, which react to changes in the internal environment; and proprioceptors, which respond to variations in movement, position, and tension. These impulses terminate in special areas of the brain, as do of those special receptors concerned with sight, hearing, smell, and taste.
Whereas most major nerves emerge from the spinal cord, the 12 pairs of cranial nerves project directly from the brain. All but 1 pair relay motor or sensory information (or both); the tenth, or vagus nerve, affects visceral functions such as heart rate, vasoconstriction, and contraction of the smooth muscle found in the walls of the trachea, stomach, and intestine.
Muscular contractions do not always cause actual movement. A small fraction of the total number of fibers in most muscles is usually contracting. This serves to maintain the posture of a limb and enables the limb to resist passive elongation or stretch. This slight continuous contraction is called muscle tone.
In 1946 Axelrod joined the laboratory of American pharmacologist Bernard Brodie at Goldwater Memorial Hospital in New York. The pair conducted research on pain-relieving drugs called analgesics. They identified a pain-relieving chemical known as acetaminophen. This drug was later developed and marketed by the drug company Johnson & Johnson under the brand-name Tylenol.
In 1949 Axelrod took a position at the National Heart Institute, a branch of the National Institutes of Health (NIH). Their Axelrod studied how the body processes certain drugs that cause behavioral changes, including amphetamines, ephedrine, and mescaline. He identified a group of enzymes that help these drugs break down in the body. These enzymes, called cytochrome-P450 monoxygenases, have been studied extensively by other scientists, particularly in cancer research.
Realizing that career advancement in the sciences requires a doctoral degree, in 1954 Axelrod took a leave of absence from his job at the National Heart Institute to attend The George Washington University. He earned his doctorate in pharmacology in 1955. That same year he was named chief of pharmacology at the National Institute of Mental Health (NIMH) another branch of NIH.
At NIMH, Joseph Axelrod began research on neurotransmitters. A nerve cell releases a neurotransmitter to spur a neighboring cell into action. In the 1950s most scientists believed that a neurotransmitter became inactive once it stimulated a neighboring cell. But Axelrod’s research found that the neurotransmitter returns to the first nerve cell, in a process known as reuptake, where it is broken down by enzymes or repackaged for reuse. This research led to the creation of a number of drugs that prevent the reuptake process, enabling a neurotransmitter to remain active for a longer period of time.
Axelrod’s research revolutionized the understanding of many mental-health disorders, including depression, anxiety, and schizophrenia. Prior to his research, psychiatry focused on the relationship of life experiences to mental health problems. But Axelrod's research proved that mental-health disorders were often the result of complicated brain chemistry. His research spurred the development of new drugs that advanced the treatment of mental-health conditions. Among these are selective serotonin reuptake inhibitors, including the antidepressants fluoxetine, sold under the brand name Prozac, sertraline(Zoloft) and paroxetine (Paxil).
The study of the biochemistry of memory is another exciting scientific enterprise, but one that can only be touched upon here. Scientists estimate that an adult human brain contains about 100 billion neurons. Each of these is connected to hundreds or thousands of other neurons, forming trillions of neural connections. Neurons communicate by chemical messengers called neurotransmitters. An electrical signal travels along the neuron, triggering the release of neurotransmitters at the synapse, the small gap between neurons. The neurotransmitters travel across the synapse and act on the next neuron by binding with protein molecules called receptors. Most scientists believe that memories are somehow stored among the brain's trillions of synapses, rather than in the neurons themselves.
Scientists who study the biochemistry of learning and memory often focus on the marine snail Aplysia because its simple nervous system allows them to study the effects of various stimuli on specific synapses. A change in the snail's behavior due to learning can be correlated with a change at the level of the synapse. One exciting scientific frontier is discovering the changes in neurotransmitters that occur at the level of the synapse.
Other researchers have implicated glucose, a sugar and insulin(a hormone secreted by the pancreas) as important to learning and memory. Humans and other animals given these substances show an improved capacity to learn and remember. Typically, when animals or humans ingest glucose, the pancreas responds by increasing insulin production, so it is difficult to determine which substance contributes to improved performance. Some studies in humans that have systematically varied the amount of glucose and insulin in the blood have shown that insulin may be the more important of the two substances for learning.
Scientists also have examined the influence of genes on learning and memory. In one study, scientists bred strains of mice with extra copies of a gene that helps build a protein called N-methyl-D-aspartate, or NMDA. This protein acts as a receptor for certain neurotransmitters. The genetically altered mice outperformed normal mice on a variety of tests of learning and memory. In addition, other studies have found that chemically blocking NMDA receptor impairs learning in laboratory rats. Future discoveries from genetic and biochemical studies may lead to treatments for memory deficits from Alzheimer's disease and other conditions that affect memory.
Alzheimer's Disease, progressive brain disorders that causes a gradual and irreversible decline in memory, language skills, perception of time and space, and, eventually, the ability to care for oneself. First described by German psychiatrist Alois Alzheimer in 1906, Alzheimer's disease was initially thought to be a rare condition affecting only young people, and was referred to as prehensile dementia. Today late-onset Alzheimer's disease is recognized as the most common cause of the loss of mental function in those aged 65 and over. Alzheimer's in people in their 30s, 40s, and 50s, called early-onset Alzheimer's disease, occurs less frequently, accountings for less than 10 percent of the estimated 4 million Alzheimer's cases in the United States.
Although Alzheimer's disease is not a normal part of the aging process, the risk of developing the disease increases as people grow older. About 10 percent of the United States population over the age of 65 is affected by Alzheimer's disease, and nearly 50 percent of those over age 85 may have the disease.
Alzheimer's disease takes a devastating toll, not only on the patients, but also on those who love and care for them. Some patients experience immense fear and frustration as they struggle with once commonplace tasks and slowly lose their independence. Family, friends, and especially those who provide daily care suffer immeasurable pain and stress as they witness Alzheimer's disease slowly take their loved one from them.
The onset of Alzheimer's disease is usually very gradual. In the early stages, Alzheimer's patients have relatively mild problems learning new information and remembering where they have left common objects, such as keys or a wallet. In time, they begin to have trouble recollecting recent events and finding the right words to express themselves. As the disease progresses, patients may have difficulty remembering what day or month it is, or finding their way around familiar surroundings. They may develop a tendency to wander off and then be unable to find their way back. Patients often become irritable or withdrawn as they struggle with fear and frustration when once commonplace tasks become unfamiliar and intimidating. Behavioral changes may become more pronounced as patients become paranoid or delusional and unable to engage in normal conversation.
Eventually Alzheimer's patients become completely incapacitated and unable to take care of their most basic life functions, such as eating and using the bathroom. Alzheimer's patients may live many years with the disease, usually dying from other disorders that may develop, such as pneumonia. Typically the time from initial diagnosis until death is seven to ten years, but this is quite variable and can range from three to twenty years, depending on the age of the onset, other medical conditions present, and the care patients receive.
The brains of patients with Alzheimer's have distinctive formations - abnormally shaped proteins called tangles and plaques - that are recognized as the hallmark of the disease. Not all brain regions show these characteristic formations. The areas most prominently affected are those related to memory.
Tangles are long, slender tendrils found inside nerve cells, or neurons. Scientists have learned that when a protein-called tau becomes altered, it may cause the characteristic tangles in the brain of the Alzheimer’s patient. In healthy brains provides structural support for neurons, but in Alzheimer's patients this structural support collapses.
Plaques, or clumps of fibers, form outside the neurons in the adjacent brain tissue. Scientists found that a type of protein, called amyloid precursor protein, forms toxic plaques when it is cut in two places. Researchers have isolated the enzyme beta-secretes, which is believed to make one of the cuts in the amyloid precursor protein. Researchers also identified another enzyme, called gamma secretes, that makes the second cut in the amyloid precursor protein. These two enzymes snip the amyloid precursor protein into fragments that then accumulate to form plaques that are toxic to neurons.
No comments:
Post a Comment