THE NERVOUS SYSTEM

Conscious and unconscious thoughts and feelings certainly must have an abode in the human body, but it is not yet possible to specify their "local habitations" with any great accuracy. In the largest sense we feel and "think" with our entire bodies. The "lan­guage of behavior" is spoken by every cell in the body. Through the performance of differ­ent functions by myriads of separate cells, the total action of the body and the pattern of human conduct become possible. But this is effective and meaningful action only when the activity of the cells, and the organs they comprise, is coordinated and integrated through the nervous and endocrine systems.

The nervous system is the essential com­munication system within the body, and it also makes possible communication between human beings. We cannot here explore all the marvelous complexities of the human nervous system, of which the brain is the signal part. But we must emphasize the continuing im­portance of a well-functioning nervous system to the characteristic behavior of the human being. There remain many unsolved myster­ies in this area. We do not know, for example, how a nerve cell (or a group of them) trans­mutes sensation into action. Since the ner­vous system carries sensation, information, and orders from one part of the body to another, there is some justification for compar­ing it with a series of interconnected tele­phone systems so long as we remember that this description is an oversimplification of its complex functions.

For convenience of understanding and de­scription, it is conventional to divide the sin­gle integrated nervous system into three ma­jor parts: peripheral, autonomic, and central.

The peripheral nervous system includes nerve trunks and end-plates (like the retina of the eye) with which the body perceives and makes contact with the outside world. These end-organs, or end-plates, may be likened to the receivers and mouthpieces of myriads of telephone instruments. The end-plates that pick up sensations are called receptors; those that deliver orders are called effectors. Sensa­tions are transmitted through sensory nerves; orders come back by way of motor nerves.

End-organs are specific for their particular sensations or reactions. Thus the eye reacts to light, the ear to sound, the nose and tongue to chemicals in solution (providing the senses of taste and smell). Human beings have far more than the traditional five senses. There are distributed on the body, for example, end-organs for hot and cold, for pressure, for pain; and there are combinations of impacts on end-organs that give a sense of vibration, balance, hunger, thirst, and other feelings.

The autonomic (or vegetative) nervous sys­tem is composed of a series of nerve relays or switchboards (ganglia) that run up and down the outside of the spinal column and their interconnecting nerves This system operates chiefly to help regulate man's basic physio­logic functions, such as digestion and respira­tion, which go on without any conscious thought or effort. There are two parts to the autonomic nervous system; they act as antag­onists of one another.

The central nervous system can be consid­ered both the central and executive office of the body's communication system. It includes the spinal cord, the brain-stem, and the brain itself. It is the brain that interprets the meaning of the sensations picked up by the end-organs of the peripheral nervous system. The cerebrum, divided into two cerebral hem­ispheres, is the largest part of the brain and the seat of man's highest intellectual and  rational  functions. In it are  localized many important brain functions, for example, a speech center.