Human physiology; an elementary text-book with special emphasis on hygiene and sanitation by Ritchie John W. (John Woodside) 1871-1943

Author:Ritchie, John W. (John Woodside), 1871-1943
Language: eng
Format: epub
Tags: Physiology
Publisher: Yonkers-on-Hudson, N.Y., World book company
Published: 1915-03-25T05:00:00+00:00

Fig. 97. A neuron.

Digitized by VjOOQIC

HUMAN- PHYSIOLOGY

will understand better after studying reflex actions, a great portion of the work of the nervous system in governing the body is done by putting the different body parts into communication with each other. In a former chapter (page 23) we have spoken of the nervous system as the ruler of the body. In reality, it resembles a telephone system as much

Fig. 98. A shows the number of wires necessary to connect twelve houses by telephone without a central office. B shows the number of wires necessary to connect the same number of houses through a central office. The number of nerve fibers that would be necessary to connect all parts of the body without a brain and spinal cord to act as a central office can hardly be imagined.

as it does a monarch. As on a telephone system the different houses are put into connection with each other through a central office, so the different parts of the body are connected through the brain and spinal cord. In many parts of the body each cell is supplied with a nerve fiber (Fig. 102) and the body has in it a perplexing network of nerves. By examining Figure 98, you can understand what a hopeless tangle the nervous system would become if an attempt were made to connect all the cells of the body with-put a brain and spinal cord to act as a central office.

Digitized by VjOOQ IC

THE NERVOUS SYSTEM

213

THE CENTRAL NERVOUS SYSTEM

The central nervous system consists of the brain, the spinal cord, and the nerves arising from the brain and cord. Twelve pairs of nerves pass out from the brain, and thirty-one pairs from the cord, putting these nerve centers in connection with all the body parts.

The Brain. The spinal cord is only a little thicker than a lead penciL The brain fills the whole cranial cavity. The

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.