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.