autonomic nervous system n.
The part of the nervous system that regulates involuntary action, as of the intestines, smooth muscle, heart, and glands, and that is divided into two physiologically and anatomically distinct, mutually antagonistic systems, the sympathetic nervous system and the parasympathetic nervous system.
The part of the nervous system that controls involuntary functions of the body (those not controlled consciously), such as digestion, the beating of the heart, and the operation of glands in the endocrine system.