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Autonomic nervous system

(Science: anatomy) 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. The part of the nervous system of vertebrates that controls involuntary actions of the smooth muscles and heart and glands.Also known as the involuntary nervous system, this part of the system executes actions unconsciously in the organism. See sympathetic and parasympathetic nervo.