d. The neurons innervating the peripheral visceral organs are distributed to
them by being included in the nerves of the PNS.
e. The sympathetic NS activates those visceral organs needed to mobilize
energy for action (example: heart) and deactivates those not needed (example: gut).
11-18. THE CRANIO-SACRAL OUTFLOW (PARASYMPATHETIC NERVOUS
a. Cell bodies of the first neurons of the parasympathetic NS make up the inter-
mediolateral gray columns in the sacral spinal cord at the S-2, S-3, and S-4 levels. See
paragraph 11-17a above for the position of the intermediolateral gray columns. Cell
bodies of the first neurons also make up four pairs of nuclei in the brainstem; these
nuclei are associated with cranial nerves III, VII, IX, and X. Here, we are speaking of
preganglionic parasympathetic neurons.
b. Cell bodies of the second neurons make up intramural ganglia within the
walls of the visceral organs. These second neurons innervate the central visceral
organs. They do NOT innervate peripheral visceral organs. Here, we are speaking of
the post-ganglionic parasympathetic neurons.
c. The parasympathetic NS has the opposite effect on visceral organs from that
of the sympathetic NS. (Example: The heart is accelerated by the sympathetic NS and
decelerated by the parasympathetic NS.)
Section VI. PATHWAYS OF THE HUMAN NERVOUS SYSTEM
(1) A pathway is the series of nervous structures utilized in the transmission
of an item of information. An example of a pathway is the reflex arc discussed in para-
(2) The brainstem is continuous with the spinal cord. Together, the
brainstem and the spinal cord are sometimes known as the neuraxis.
b. General Categories of Neural Pathways.
(1) Sensory pathways. A sensory pathway is a series of nervous structures
used to transmit information from the body to the CNS. Upon arrival in the CNS, these
pathways ascend (go up) the neuraxis to the brain.