AUTONOMIC NERVOUS SYSTEM
The autonomic nervous system (ANS) is the
portion of the PNS that functions independently,
automatically, and continuously, without conscious
effort. It helps to regulate the smooth muscles, cardiac
muscle, digestive tube, blood vessels, sweat and
digestive glands, and certain endocrine glands. The
autonomic nervous system is not directly under the
control of the brain but usually works in harmony with
the nerves that are under the brain's control. The
autonomic nervous system includes two subdivisions
(the sympathetic and parasympathetic nervous
systems) that act together.
The sympathetic nervous system's primary
concern is to prepare the body for energy-expending,
stressful, or emergency situations. On the other hand,
the parasympathetic nervous system is most active
under routine, restful situations. The parasympathetic
system also counterbalances the effects of the
sympathetic system, and restores the body to a resting
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POSTERIOR
VIEW
CERVICAL
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Figure 1-46.—Spinal nerves.
