Autonomic Nervous System

The nervous system responsible for regulating automatic bodily processes, such as breathing and heart rate. The autonomic system also involves the processes of metabolism, or the storage and expenditure of energy.

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 linking the sense organs, muscles, and glands to the central nervous system). The structures of the peripheral nervous system are further subdivided into the autonomic nervous system (automatic bodily processes) 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 normal, nonstressful situations. For example, after eating, the digestive process begins, whereby nutrients are taken from the food and stored in the body. The flow of blood increases to the stomach and intestines while at the same time the heart rate decreases and saliva is secreted. The parasympathetic division also mediates sexual arousal, even though most parasympathetic functions lead to lower overt 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, the lungs expand to hold more oxygen, the pupils dilate, and blood flows to the muscles.

While the autonomic nervous system normally functions quite appropriately, abnormalities can appear. In anxiety disorders, for example, certain somatic (bodily) symptoms such as muscular tension, hyperventilation, increased heart rate, and high blood pressure are increased, posing the body for attack. This physiological response can lead to such additional maladies as headaches and digestive problems. At times, parasympathetic responses occur simultaneously. In extreme 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 prior to schizophrenic breakdown.

For decades, scientists believed that autonomic processes were not amenable to voluntary control. In recent years, 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.