The autonomic nervous system (ANS) is that portion of the nervous system
generally concerned with commands for smooth muscle tissue, cardiac muscle tissue, and
glands.
a. Visceral Organs.
(1) Definition. The term visceral organs may be used to include:
(a) The various hollow organs of the body whose walls have smooth muscle
tissue in them. Examples are the blood vessels and the gut.
(b) The glands.
(2) Distribution. The visceral organs are located in the central cavity of
the body (example: stomach) and throughout the periphery of the body (example: sweat
glands of the skin).
(3) Control. It has always been thought that the control of visceral
organs was "automatic" and not conscious. However, recent researches indicate
that proper training enables a person to consciously control some of the visceral organs.
b. Efferent Pathways. Earlier, we said that each neuron in the PNS
extended the entire distance from the CNS to the receptor or effector organ. In the ANS,
there are always two neurons (one after the other) connecting the CNS with the visceral
organ. The cell bodies of the second neurons form a collection outside the CNS, called a
ganglion.
(1) The first neuron extends from the CNS to the ganglion and is therefore
called the preganglionic neuron.
(2) Cell bodies of the second neuron make up the ganglion. The second
neuron's processes extend from the ganglion to the visceral organ. Thus, the second neuron
is called the post-ganglionic neuron.
c. Major Divisions of the Human ANS. The efferent pathways of the
ANS fall into two major divisions:
(1) The thoraco-lumbar outflow (sympathetic nervous system).
(2) The cranio-sacral outflow (parasympathetic nervous system).
d. Major Activities of the Human ANS.
(1) The ANS maintains visceral activities in a balanced or stable state.
This is called homeostasis.
(2) When subjected to stress, such as a threat, the body responds with the
"fight-or-flight reaction." That is, those activities of the body necessary for
action in an emergency are activated and those not necessary are deactivated. This is the
primary function of the sympathetic portion of the ANS.
Primary Content Providers: The U. S. Army, The
U.S. Navy
Ancillary Content and Online Version: David L. Heiserman
Publisher: SweetHaven Publishing Services
