ision.

The efferent nerves are those which convey the nervous impulse outward from
the nerve centers, and they are further classified according to the
function of their respective centers. For example: Motor fibers carry the
impulse from the nerve center to a muscle to cause contraction. Vasomotor
fibers carry the impulse to the muscular tissue in the blood vessels, which
regulates their caliber. The secretory fibers convey the impulse to the
cells of the glands and excite the activity of the gland, and its
particular product is secreted or evolved, as, for instance, milk in the
mammary gland. Inhibitory fibers control or inhibit the action of the organ
to which they are distributed, as, for instance, the heart.

Nerve centers may be considered as a collection or group of nerve cells.
Both the cerebrospinal and the sympathetic divisions have nerve centers.
The centers derive their special names from their functions. The brain is
the great center of the nervous system, as it is the center of intelligence
and perception. The centers of all the special senses, as well as the
centers of various functions, are located in different parts of the brain.
Nerve centers also exist in the spinal cord and in connection with the
sympathetic system.

A nerve is a cord consisting of a certain number of fibers of nerve tissue,
inclosed in a sheath of connective tissue. Nerves divide and subdivide,
sending off branches, which ramify in all parts of the body, and, as they
near their terminations, they contain but one or two fibers.

The brain and spinal cord are contained within a bony canal, which forms a
protective covering for them.

The spinal cord, or spinal marrow, lodged within the spinal canal, or
hollow of the backbone, is continuous with the brain anteriorly, and
terminates in a point in the sacrum (that part of the spinal column which
immediately precedes the tail). The spinal cord gives off branches at each
of the spaces between the segments of the backbone. These branches form
nerve trunks which carry both sensory and motor impressions and impulses.
The spinal cord is a grand nerve trunk to carry messages to or from the
brain and to and from the reflex centers contained within itself.

The brain is contained within the cavity of the skull and is continuous
with the spinal cord; there is nothing to mark the place where one leaves
off and the other begins. The brain is the seat of reason and intelligence.
Voluntary effort