Autonomic Nervous System

The autonomic nervous system is the part of the nervous system responsible for regulating automatic bodily processes, such as breathing and heart rate. It also regulates the processes of metabolism, which is the systematic storage and expenditure of energy within an organism.

The nervous system consists of two main structures, the central nervous system (the brain and the spinal cord) and the peripheral nervous system (the sense organs and the nerves that link the sense organs, muscles, and glands to the central nervous system). The structures of the peripheral nervous system are subdivided into the autonomic nervous system and the somatic nervous system.

The part of the autonomic nervous system that controls the storage of energy, called anabolism, is the parasympathetic division. Parasympathetic, or anabolic, activities involve bodily functions that occur in typical, non-stressful situations. For example, after eating, the digestive process begins. Nutrients are taken from food and stored in the body. The flow of blood increases to the stomach and intestines while the heart rate decreases and saliva is secreted.

The parasympathetic division mediates sexual arousal, although most parasympathetic functions lead to lower arousal levels. Sexual climax is controlled by the sympathetic division.

In general, sympathetic processes reverse parasympathetic responses. The sympathetic division is activated when the body mobilizes for defense or in response to stress. Such processes use energy stored during anabolism; this use of energy is referred to as catabolism. In defensive situations, the heart rate increases, lungs expand to hold more oxygen, the pupils dilate, and blood flows to the muscles and away from the core. Particular hormones mediate functions in the sympathetic and parasympathetic nervous systems.

Although the autonomic nervous system generally functions quite predictably, abnormalities may create psychological problems. In anxiety disorders, for example, particular somatic (bodily) symptoms such as muscular tension, hyperventilation, increased heart rate, and high blood pressure increase without a specific external stimulus. The individual becomes hypervigilant. The anxious person feels chronically poised for attack and prepared for danger. This physiological response often leads to symptoms such as headaches and digestive problems. At times, parasympathetic responses occur spontaneously. In extremely stressful situations, for example, an individual may experience involuntary discharge of the bladder and bowels. Some research has also indicated deficiencies in autonomic arousal processes in psychiatric patients immediately prior to an episode of psychosis.

For decades, scientists believed that autonomic processes were not amenable to voluntary control. Subsequently, however, people with heart problems have learned to modify heart rates, and headache sufferers have learned to modify blood flow to relieve pain through biofeedback techniques. New imaging techniques helped patients see the results of their behavioral changes directly as they learned to modulate their breathing or lower their heart rate.

See also Anxiety/anxiety disorders; Biofeedback ; Brain ; Central nervous system ; Hypothalamus .



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