Publisher Summary
This chapter describes the functions of nervous system. The nervous system is concerned and inquisitive about what goes on around it. It monitors light, sound, smell, and the feel of things. It monitors every physical stimulus known. Such monitoring is carried out by specialized receptors. Eyes capture light and convert it into brain language; ears hear sounds; the nose collects smells; hands, legs, and the whole body surface is sensitive to touch, pressure, and vibration. The receptors of these body parts report to the brain, and the impressions they bring result in behavior: a simple reflex, an association or simply a mental note of what has transpired. The job of the nervous system is to make sense of the stimuli that it receives. The body and nervous system are partners, and each depends on the other. The nervous system acts through the body, and it maintains and cares for its home, its avenue of access to the external world.
I Introduction
⌠We think of ourselves and others as engaged from moment to moment in doing this or that. That is a convenience of speech. Each of us at any moment of the waking day is a whole bundle of acts simultaneously proceedingâŚ. In no case does any other of all the doings of the moment disturb the one focal doing. We are each therefore at any moment a pattern of active doing; a single pattern of pieces all subordinate to one keypiece. No other part of the pattern is allowed to disturb the keypiece of the pattern. Should it do so then the pattern changes and the disturbing piece becomes usually the keypiece of a new pattern which supplants the previous. The keypiece is the crown of the unified doing of the moment (Sherrington, 1946, pp. 172â173).
Our responses are the products of the nervous system acting through the body. We walk, talk, touch, look, listen, even laugh, in so many ways that our total responses can only be summed up as behaviorâbehavior designed for the moment. Our nervous system provides an immense repertoire of specific behavior, together with built-in contingency plans. It is at one and the same time reporter, editor, producer, file clerk and delivery boy for our moment by moment events. It collects critical newsworthy information, analyzes it, modifies it in relation to our interests, keeps a record of all transactions and delivers a report to our muscles and glands so we may act. In our behavior we see reliability, precision and versatilityâprograms of living designed specifically for us. Yet our reactions to many things are identical, universals of response shared so commonly among all men and women that we are able to analyze the biological basis of behavior from them.
In this text we shall concern ourselves with the biological bases of behavior, the âhows,â âwhys,â and âso whats.â How does the nervous system administer that miraculous performance called behavior? What is the role of the subcomponents of behavior in relationship to its overall plan? These questions are challenging ones, and at present we really do not have all the answers. But in behavioral neuroscience we are attaining more and more exciting findings. The prospects for the future are very bright indeed. Neurobiology is still a very young field, and much is happening every day. In this text we shall take you into the nervous system and from within try to show how it pilots our behaviors. However, prior to embarking on this journey and seeking out the ways the nervous system controls behavior, we would do well to put our mission into perspective. Just what does the nervous system do?
II Functions of the Nervous System
A The Nervous System Organizes and Directs Motor Responses
We can start at the endâourselves moving. Much behavior is purposeful movement, and the nervous system is the executor of this movement. As Lord Adrian (1955), a revered neurophysiologist and one of the founding fathers of the study of the brain, once wrote, âThe chief function of the nervous system is to send messages to the muscles which will make the body move effectively as a whole.â Such effective, unitary movement has extraordinarily diverse components. Embodied in it are some of the simplest and some of the most complex behavioral responses. The simplest of these is a reflex. A tap to the knee elicits a kick of the leg, the prick of a pin on a finger brings its withdrawal. Patterns of movement, whether those of a Mozart playing a concerto or of you and me simply talking, are the integrated result of many influences.
But even holding still is a tremendous motor task. We might not normally think about it, but one of the jobs of the nervous system is simply to maintain posture. The nervous system is constantly at work maintaining our bodyâs posture to keep us upright. It issues a continuing program of signals so that the appropriate muscles maintain the appropriate tensions. No robot yet invented even approximates the skill of our nervous system in moving a body or keeping it erect.
Motion is totally unified: the body moves as a whole in a highly coordinated manner.
The individual cannot be the seat of two focal acts at once. In the pattern of doing of the moment the focal act has commonly a number of satellite acts contributory to it, the keypiece of the pattern. A score of contributory acts of posture, and of sensory adjustment, secondarily contribute to give speed or steadiness or precision to the focal act, and of these each one can be and probably has been at other moments a centre of awarenessâŚ. Elsewhere focal mind is exemplified by perception or cognition, but here we see it wedded to motricity, âdoingâ a motor act (Sherrington, 1946, p. 173).
We can see then that the answer to âso whatâ and âwhyâ is that motion gives us behavior.
How? Behind the scenes, under our skin so to speak, driving our muscles are teams of nerve cells playing out their patterns of activity from the spinal cord and instructing the muscles, through long nerve fibers, to contract and relax. Those teams prompt muscles to action, pulling on our bones in different ways so smoothly we scarcely realize the underlying structure is bone and muscle. This neuronal activity and the teams of neurons playing it out give us purposeful motion.
B The Nervous System Monitors Its Outside World
The nervous system is concerned and inquisitive about what goes on around it. It monitors light, sound, smell and âthe feelâ of things. In brief, it monitors every physical stimulus known. Where pertinent, it even looks at magnetic fields; birds use such information to migrate.
Such monitoring is carried out by specialized receptors. Eyes capture light and convert it into brain language; ears hear sounds; the nose collects smells; hands, legs, and, in fact, our whole body surface is sensitive to touch, pressure and vibration. The receptors of these body parts report to the brain, and the impressions they bring result in behavior: a simple reflex, an association or perhaps simply a mental note of what has transpired. The job of the nervous system is to make sense of the stimuli which it receives. âWhy?â To monitor the environment. âHow?â With receptors. âSo what?â To adjust behavior in a meaningful way to the world about.
Much of what exists in the external world, even in our immediate surroundings, we never perceive, at least at a conscious level. How do we select certain things for our attention over others? If we become deeply interested in one particular thing, chances are good that we will miss others. Yet at the same time the important things never go unnoticedâthey are just too impressive. Try sitting on a tack and not noticing it. Pain, as we are all too aware, emblazons itself upon our brains and calls us to action. The job of the nervous system, then, is to put stimuli in the appropriate perspective. Mind is focal in collecting and integrating stimuli and in producing responses.
C Learning and Remembering
Learning is the most important thing we do. What we perceive becomes, in many cases, part of us so that our present is a cumulative function of the past. We must learn or we cannot become even the feeblest masters of our destinies. Creatures, such as an amoeba, for example, unblessed with anything like our powerful memories, meander about looking for morsels of food. Merely eating consumes nearly full time for simple creatures, but occupies only a fraction of our day because of our superior nervous system and physiology. Learning, not eating, is our dominant mechanism of survival, giving self-assurance and economy, as well as sustenance, to daily living. It is what we learn individually and are finally able to put into practice that makes us each so different. It is also our combined efforts that make our society and give us a rich culture. So perhaps we can see why we can say that learning is the most important thing we do.
How do we learn? In many ways, only a few of which are really known, the nervous system builds into its structure relics of its past. In order to study learning and memory, we need to understand the basic cellular operations of the memory system. For now, we can say that somehow neural circuitry encodes the realities it has experienced and the logic and associations that have served us so well.
Despite all we know, everything stamped into the files of our brain, and all we can do from what we have learned, the mindâs product is still focal, unitary action, as Sherrington saw. We still strive to make one decision, generate one thought, do one thing; no other part of the pattern is allowed to disturb the focus.
D Thinking and Personality
We use our brain to generate and relate thoughts. Thinking takes individual events and generates conceptsâideas. Ideas then become their own reality as they are put into practice....