Autonomic nervous system:A part of the nervous system that regulates keyinvoluntaryfunctions of the body, including the activity of the heartmuscle; the smooth muscles, including the muscles of the intestinal tract; and the glands. Theautonomic nervous systemhas two divisions: thesympathetic nervous system, which accelerates theheart rate, constrictsbloodvessels, and raisesblood pressure, and theparasympathetic nervous system, which slows the heart rate, increases intestinal andglandactivity, and relaxes sphincter muscles.
