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CHAPTER SEVEN

THE NERVOUS SYSTEM

In the human body just as in a community of human beings, there must be some means of communication. In communities the telephone, the telegraph and radio serve this end. In the human body the nervous system serves this and many other needs, for it controls human thought and conduct; gives us the power to understand and appreciate the world in which we live; to see, to hear, to move, to eat and to talk. The nervous system is the chief control of our internal organs and is constantly supplying the body with knowledge of its environment, interpreting this knowledge and adjusting the body to it. The study of the nervous system is called NEUROLOGY.

The nervous system is composed of central masses of nerve tissue, all connected by nerve fibers which branch out to all parts of the body.

A nerve is a bundle of round or flattened fibers or processes of nerve tissue originating in the brain and spinal cord.

Nerve tissue is composed of cells of varying size and shape called NEURONS which extend themselves in chains often as much as two or three feet. It possesses the power of (1) excitability, that is it responds to to stimulation; and (2) conductivity, that is the power to transmit impulses to other cells. It is composed of two kinds of nerve material, the GRAY and WHITE MATTER. The cells make up the gray matter and the fibers constitute the white matter.

Like the muscles, nerves may be separated into fibers. These fiibers [[fibers]] are bound together into nerve trunks by connective tissue containing blood vessels, lymph spaces and lymphatic glands.

Functions of the Nervous System

1. Serves as a means of communication between different parts of the body.
2. Controls human thought and action.
3. Gives the power to see, move, hear and talk.
4. Chief control of internal organs.
5. Supplies body with knowledge of environment.
6. Interprets this knowledge and adjusts body to it.

TEXT BOOK OF BEAUTY CULTURE

Nerves are classified as Motor, Sensory and Mixed according to their function.

Nerves May Be Stimulated:

1. Chemically (salts, acids, alkali).
2. Mechanically (Massage).
3. Thermally (Heat).
4. Electrically (Violet Ray).
5. By their own impulses.

The brain and Spinal Cord are the two principal organs of the nervous system. From these centers nerves pass out through small openings in the skull and spinal column and are distributed to all parts of the body, dividing and subdividing until they become threadlike filaments invisible to the human eye. The nervous system is divided into two general parts:

1. Cerebrospinal or Voluntary System.
2. Autonomic, Sympathetic or involuntary System.

The voluntary system of nerves controls all the impulses sent out to the voluntary muscles of the body. It is also known as the Central Nervous System and consists of the brain and the spinal cord and the nerves from these organs, called the Cranial and Spinal nerves, extending to all parts of the body. They constitute the PERIPHERAL SYSTEM.

The SYMPATHETIC or INVOLUNTARY SYSTEM of nerves are so called because the body structures they serve are not under voluntary control but are self-acting. These nerves control the involuntary muscles which affect our breathing, digestion, blood circulation, eye action, etc., and control the body during sleep and periods of unconsciousness.

The Cranial Nerves

There are twelve pairs of cranial nerves which emerge from the under surface of the brain and pass through the opening in the base of the skull. They originate in those divisions of the brain known as the cerebrum and the Medulla Oblongota and are classified as motor, sensory and mixed nerves, containing both motor and sensory nerve fibers. The cranial nerves are named numerically according to the order in which they arise from the brain and also by names which describe their nature, function, or distribution.

1. Olfactory-The nerve of smell. (Sensory.)
2. Optic-The nerve of sight. (Sensory.)