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.
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