Autonomic Nervous System
The autonomic nervous system is a part of the nervous system once thought to be functionally independent of the brain. However, this is now known not to be the case. The autonomic nervous system regulates key functions of the body including the activity of the heart muscle (see below), the smooth muscles (e.g., the muscles of the intestinal tract), and the 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.