brain, spinal cord, and nerve disorders
Overview of the Autonomic Nervous System
Function of the autonomic nervous system
The autonomic nervous system controls internal body processes such as the following: Blood pressure Heart and breathing rates Body temperature Digestion Metabolism (thus affecting body weight) The About Body Water and The production of body fluids (saliva, sweat, and tears) Urination Defecation Sexual response Many organs are controlled primarily by either the sympathetic or the parasympathetic division. Sometimes the two divisions have opposite effects on the same organ. For example, the sympathetic division increases blood pressure, and the parasympathetic division decreases it. Overall, the two divisions work together to ensure that the body responds appropriately to different situations. Generally, thesympathetic divisiondoes the following: Prepares the body for stressful or emergency situations—fight or flight Thus, the sympathetic division increases heart rate and the force of heart contractions and widens (dilates) the airways to make breathing easier. It causes the body to release stored energy. Muscular strength is increased. This division also causes palms to sweat, pupils to dilate, and hair to stand on end. It slows body processes that are less important in emergencies, such as digestion and urination. Theparasympathetic divisiondoes the following: Controls body process during ordinary situations. Generally, the parasympathetic division conserves and restores. It slows the heart rate and decreases blood pressure. It stimulates the digestive tract to process food and eliminate wastes. Energy from the processed food is used to restore and build tissues. Both the sympathetic and parasympathetic divisions are involved in sexual activity, as are the parts of the nervous system that control voluntary actions and transmit sensation from the skin ( Somatic nervous system ). Two main chemical messengers (neurotransmitters) are used to communicate within the autonomic nervous system: Acetylcholine Norepinephrine Nerve fibers that secrete acetylcholine are called cholinergic fibers. Fibers that secretenorepinephrineare called adrenergic fibers. Generally, acetylcholine has parasympathetic effects andnorepinephrinehas sympathetic effects. However, acetylcholine has some sympathetic effects. For example, it sometimes stimulates sweating or makes the hair stand on end. 