NERVOUS SYSTEM, AUTONOMIC

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, which accelerates the heart rate, constricts blood vessels, and raises blood pressure; and (2) the parasympathetic nervous system, which slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles.