(c) Within the spinal cord, there is a special neuron connecting the
afferent neuron to the efferent neuron. This special connecting neuron is called the
internuncial neuron, or interneuron.
INTER = between
NUNCIA = messenger
INTERNUNCIAL = the carrier of information between
(d) The efferent (motor) neuron carries the appropriate command from
the spinal cord to the reacting muscle.
(e) The reacting muscle is called the effector organ.
Section V. THE AUTONOMIC NERVOUS SYSTEM (ANS)
The autonomic nervous system (ANS) is that portion of the nervous system
generally concerned with commands for smooth muscle tissue, cardiac muscle tissue,
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