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 neurotransmitter throughout the parasympathetic system is acetylcholine (ACh) 1.
Gross anatomy
The cranial portion of the parasympathetic nervous system arises from four cranial nerve nuclei in the brainstem (see head and neck ganglia):
Edinger-Westphal nucleus in the midbrain contributes parasympathetic fibers to the oculomotor nerve that synapse at the ciliary ganglion; postganglionic fibers course in the short ciliary nerves to the ciliary body and sphincter pupillae, producing accommodation and pupillary constriction respectively
-
superior salivary nucleus in the pons contributes parasympathetic fibers to the facial nerve which synapse in the submandibular ganglion and pterygopalatine ganglion
postganglionic fibers from the submandibular ganglion course with the nervus intermedius and then the chorda tympani of the facial nerve supplying secretomotor afferents to the sublingual and submandibular salivary glands
postganglionic fibers from the pterygopalatine ganglion course with the greater superficial petrosal nerve of the facial nerve supplying secretomotor afferents to the lacrimal gland and mucosal glands in the nose, nasopharynx, sinuses and soft palate
inferior salivary nucleus in the pons contributes parasympathetic fibers to the glossopharyngeal nerve that synapse in the otic ganglion. Postganglionic fibers course with the auriculotemporal nerve (trigeminal mandibular division) supplying secretomotor afferents to the parotid gland
dorsal vagal nucleus in the medulla contributes parasympathetic fibers to the vagus nerve which synapse in the cardiac, renal, aorticorenal, celiac, superior mesenteric, inferior mesenteric and superior hypogastric plexuses; postganglionic fibers distribute from these autonomic plexuses through the heart, esophagus and lungs in the chest and most of the abdominal and pelvic viscera
The sacral portion of the parasympathetic nervous system 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.