autonomic nervous system
In mammals, the part of the nervous system that controls those functions not controlled voluntarily, including the heart rate, activity of the intestines, and the production of sweat.
There are two divisions of the autonomic nervous system. The sympathetic system responds to stress, when it speeds the heart rate, increases blood pressure, and generally prepares the body for action. The parasympathetic system is more important when the body is at rest, since it slows the heart rate, decreases blood pressure, and stimulates the digestive system.
At all times, both types of autonomic nerves carry signals that bring about adjustments in visceral organs. The actual rate of heartbeat is the net outcome of opposing signals. Today, it is known that the word ‘autonomic’ is misleading – the reflexes managed by this system are actually integrated by commands from the brain and spinal cord (the central nervous system).
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