Parasympathetic nervous system (PSNS)

The parasympathetic nervous system (PSNS) is one of the two main divisions of the autonomic nervous system, primarily responsible for the body's 'rest and digest' activities that occur when the body is at rest (StatPearls, NBK553141). It functions to maintain homeostasis by slowing the heart rate, increasing intestinal and glandular activity, and relaxing sphincter muscles in the gastrointestinal tract (Wikipedia, Parasympathetic nervous system). Anatomically, it originates from the cranial nerves and the sacral spinal cord, utilizing acetylcholine as its primary neurotransmitter at both preganglionic and postganglionic synapses (NIH, Autonomic Nervous System). While the PSNS is a physiological system rather than a single molecular target, its individual components—such as muscarinic and nicotinic receptors—are critical targets for drugs treating conditions like glaucoma, overactive bladder, and bradycardia. Dysregulation of the PSNS, often referred to as dysautonomia, can lead to significant clinical manifestations including orthostatic hypotension, gastroparesis, and impaired pupillary responses (PubMed, PMC5859128). Consequently, pharmacological intervention often aims to either mimic or inhibit parasympathetic activity to restore functional balance.

Other names

Craniosacral divisionCholinergic nervous systemRest and digest system

Pharmacological modulation of the parasympathetic nervous system occurs primarily through the agonism or antagonism of muscarinic and nicotinic acetylcholine receptors, or via the inhibition of the enzyme acetylcholinesterase to increase the concentration and duration of action of endogenous acetylcholine at the synaptic cleft (StatPearls, NBK538239).