I. Introduction

II. Functions of the Nervous System

III. What the Nervous System Does

References

A The Nervous System Organizes and Directs Motor Responses

We can start at the end—ourselves 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, “The chief function of the nervous system is to send messages to the muscles which will make the body move effectively as a whole.” 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 body’s 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.

We can see then that the answer to “so what” and “why” 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 “the feel” 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. “Why?” To monitor the environment. “How?” With receptors. “So what?” 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 unnoticed—they 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...