Autonomic Nervous System

About the Autonomic Nervous System

The autonomic nervous system is the part of the peripheral nervous system that regulates bodily functions largely without conscious control, including heart rate, blood pressure, breathing rate, digestion, pupil size, sweating, urination, and sexual arousal. It has two main divisions that often act in opposition. The sympathetic division, arising from the thoracic and lumbar spinal cord, prepares the body for action in the classic fight or flight response, increasing heart rate, dilating airways and pupils, and diverting blood to muscles. The parasympathetic division, arising from the brainstem and sacral spinal cord and carried largely by the vagus nerve, promotes rest and digest functions, slowing the heart and stimulating digestion. The enteric nervous system, a vast network of neurons in the gut wall, is often considered a third division. Disorders of autonomic function, called dysautonomias, include orthostatic hypotension and postural orthostatic tachycardia syndrome, and autonomic neuropathy is a recognized complication of diabetes.