3. STRUCTURAL ELEMENTS OF THE NERVOUS SYSTEM
It will help in understanding both the structure and the working of the nervous
system to keep in mind that it contains but one fundamental unit of structure.
This is the neurone. Just as the house is built up by adding brick upon brick, so
brain, cord, nerves and organs of sense are formed by the union of numberless
neurones.
FIG. 6.—Neurones in different stages of development, from a to e. In a, the elementary cell
body alone is present; in c, a dendrite is shown projecting upward and an axon downward.—
After DONALDSON.The Neurone.—What, then, is a neurone? What is its structure, its function,
how does it act? A neurone is a protoplasmic cell, with its outgrowing fibers.
The cell part of the neurone is of a variety of shapes, triangular, pyramidal,
cylindrical, and irregular. The cells vary in size from 1/250 to 1/3500 of an inch
in diameter. In general the function of the cell is thought to be to generate the
nervous energy responsible for our consciousness—sensation, memory,
reasoning, feeling and all the rest, and for our movements. The cell also provides
for the nutrition of the fibers.