The parasympathetic nervous system (PNS) is 1 of the 2 functionally distinct and continuously active autonomic nervous system (ANS) divisions. It opposes the other, the sympathetic nervous system (SNS). The parasympathetic nervous system predominates in quiet “rest and digest” conditions. In contrast, the sympathetic nervous system drives the “fight or flight” response in stressful situations (see Diagram. Diagram of Efferent Sympathetic (red) and Parasympathetic (blue) Nervous System). The main purpose of the PNS is to conserve energy that can be used later and to regulate bodily functions like digestion and urination.
Copyright © 2025, StatPearls Publishing LLC.