Autonomic nervous system
Autonomic nervous system, certain sections of the brain, spinal cord, and nerve pathways that govern the activity of a number of organs, making them function largely independently of conscious control. The autonomic nervous system regulates the organs of the chest (heart and lungs), the abdomen (stomach, intestine, liver, etc.), the pelvis, and many other organs and tissues of the body, including the blood vessels and skin. By contrast, the somatic nervous system comprises those parts of the brain, spinal cord, and nerve pathways that respond to the external environment, and are under voluntary control. The autonomic nervous system governs the processes that serve to maintain the individual and the species: metabolism, growth, reproduction, respiration, nutrition and digestion, the functioning of the heart and blood vessels, the excretion of waste products, temperature control, etc. An intricate system of nuclei and nerve pathways in the brain regulates the workings of the various organs. In the hypothalamus lie dozens of nuclei and pathways that exert a controlling influence over such basic life functions as eating and drinking behavior, temperature regulation, and the percentage of sugars, fats, and water in the blood. The autonomic nervous system is also involved in emotional response. Emotions can give rise to quickening of the heartbeat, changes in breathing patterns, increased secretion of gastric acid in the stomach, and alterations in the secretory pattern of the gallbladder. Malfunction of the autonomic nervous system can easily lead to serious disturbances in the functioning of an organ. Often a stomach ache is caused by the malfunction of one of the subsystems of the autonomic nervous system. The autonomic nervous system can be divided into the sympathetic and the parasympathetic systems, which in general produce opposite effects on various organs.
See also: Nervous system.