Parasympathetic nervous system

Last revised by Craig Hacking on 17 Oct 2022

The parasympathetic nervous system (PaNS/PNS), mediated by the head and neck ganglia and pelvic splanchnic nerves, is a major division of the autonomic nervous system. It is composed of general visceral afferent and efferent axons that allow for involuntary control of bodily functions via several cranial nerve nuclei in the brainstem and the sacral segments of the spinal cord.

The overarching function of the parasympathetic system is to counteract the sympathoadrenal effects of the sympathetic nervous system. The major preganglionic neurotransmitter in the parasympathetic system is acetylcholine (ACh) whereas the major preganglionic neurotransmitter in the sympathetic system is norepinephrine (norepinephrine). The major postganglionic neurotransmitter is norepinephrine except for sweat glands which are cholinergic. 

Gross anatomy

The cranial portion of the PaNS arises from four cranial nerve nuclei in the brainstem (see head and neck ganglia):

The sacral portion of the PaNS arises from the grey matter of the sacral segments of the spinal cord at the level of S2–S4. These preganglionic fibers form the pelvic splanchnic nerves which synapse in the inferior hypogastric plexus. Some fibers pass through this plexus to the inferior mesenteric and superior hypogastric plexuses. Postganglionic fibers distribute through the structures of the hindgut and urogenital organs.

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Cases and figures

  • Figure 1: ANS (Gray's illustration)
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  • Figure 2: ciliary ganglion (Gray's illustrations)
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  • Figure 3: pterygopalatine ganglion (Gray's illustrations)
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  • Figure 4: submandibular ganglion (Gray's illustrations)
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  • Figure 5: otic ganglion (Gray's illustrations)
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