(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.
(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).
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