Neurons that are not under conscious control, comprising two antagonistic components, the sympathetic and parasympathetic nervous systems.
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.
2. The parasympathetic nervous system slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles.
(03 Jul 1999)