Of, pertaining to, or designating one of the major divisions of the autonomic nervous system: The parasympathetic nervous system is distinguished from the sympathetic system by its place of origin, its use of acetylcholine as a transmitter, and its general association with rest and recuperation rather than alertness.

The part of the involuntary nervous system which serves to slow the heart rate, increase intestinal and glandular activity, and to relax the sphincter muscles.

The parasympathetic nervous system, together with the sympathetic nervous system, constitutes the autonomic nervous system.

The autonomic nervous system is the part of the nervous system which regulates key involuntary functions of the body, including the activity of the heart muscle; the smooth muscles, including the muscles of the intestinal tract; and the glands.