Autonomic Nervous System

part of the nervous system which controls involuntary bodily functions

The autonomic nervous system (ANS) (or visceral nervous system) is the part of the peripheral nervous system that acts as a control system, maintaining homeostasis in the body. These maintenance activities are primarily performed without conscious control or sensation. The ANS has far reaching effects, including: heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils, micturition - (the discharge of urine), and erection. Whereas most of its actions are involuntary, some ANS functions work in tandem with the conscious mind, such as breathing. Its main components are its sensory system, motor system (comprised of the parasympathetic nervous system and sympathetic nervous system), and the enteric nervous system.
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Autonomic nervous system n. The part of the nervous system that regulates involuntary action, as of the intestines, smooth muscle, heart, and [more]Autonomic nervous system - Community and Resources

Noun
1. the part of the nervous system of vertebrates that controls involuntary actions of the smooth muscles and heart and glands
(synonym) ANS
(hypernym) neural structure
(part-holonym) nervous system, systema nervosum
(part-meronym) autonomic ganglion

Part of the nervous system once thought functionally independent of the brain. The autonomic nervous system regulates key functions including the activity of the cardiac (heart) muscle, smooth muscles (e.g., of the gut), and glands. The autonomic nervous system has two divisions: (1) the sympathetic nervous system that accelerates the heart rate, constricts blood vessels, and raises blood pressure; and (2) the parasympathetic nervous system slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles.

adjective
which governs itself independently

autonomic nervous system = nervous system formed of ganglia linked to the spinal column, which regulates the automatic functioning of the main organs of the body, such as the heart and lungs, and which works when a person is asleep or even unconscious
see also PARASYMPATHETIC SYSTEM, SYMPATHETIC SYSTEM