- Autonomic nervous system
- Part of the nervous system that was once thought to be functionally independent of the brain. The autonomic nervous system regulates key functions of the body including the activity of the heart muscle (see below), the smooth muscles (e.g., the muscles of the intestinal tract), and the glands. The autonomic nervous system has two divisions: (1) the sympathetic nervous system that accelerates the heart rate, constricts blood vessels, and raises blood pressure; and (2) the parasympathetic nervous system slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles. The autonomic system, together with the SA (sinoatrial) and AV (atrioventricular) nodes, is a major element in the cardiac conduction system, the system that controls the heart rate. This stunningly designed system generates electrical impulses and conducts them throughout the muscle of the heart, stimulating the heart to contract and pump blood. The SA node is the heart's natural pacemaker. The SA node consists of a cluster of cells that are situated in the upper part of the wall of the right atrium (the right upper chamber of the heart). The electrical impulses are generated there. The SA node is also called the sinus node. The electrical signal generated by the SA node moves from cell to cell down through the heart until it reaches the AV node, a cluster of cells situated in the center of the heart between the atria and ventricles. The AV node serves as a gate that slows the electrical current before the signal is permitted to pass down through to the ventricles. This delay ensures that the atria have a chance to fully contract before the ventricles are stimulated. After passing the AV node, the electrical current travels to the ventricles along special fibers embedded in the walls of the lower part of the heart. The autonomic nervous system controls the firing of the SA node to trigger the start of the cardiac cycle.
The autonomic nervous system can transmit a message quickly to the SA node so it in turn can increase the heart rate to twice normal within only 3 to 5 seconds. This quick response is important during exercise when the heart has to increase its beating speed to keep up with the body's increased demand for oxygen.
* * *autonomic nervous system n a part of the vertebrate nervous system that innervates smooth and cardiac muscle and glandular tissues and governs involuntary actions (as secretion, vasoconstriction, or peristalsis) and that consists of the sympathetic nervous system and the parasympathetic nervous system called also vegetative nervous system compare CENTRAL NERVOUS SYSTEM, PERIPHERAL NERVOUS SYSTEM
* * *the portion of the nervous system concerned with regulation of the activity of cardiac muscle, smooth muscle, and glandular epithelium; usually restricted to the two visceral efferent peripheral components, the sympathetic nervous system and the parasympathetic nervous system. Called also divisio autonomica systematis nervosi peripherici [TA], pars autonomica systematis nervosi peripherici [TA alternative], visceral nervous system, autonomic division of peripheral nervous system, and autonomic part of peripheral nervous system. See Plate 42.
PLATE 42 AUTONOMIC NERVOUS SYSTEM
Medical dictionary. 2011.
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Autonomic nervous system — The autonomic nervous system Blue = parasympathetic Red = sympathetic Latin divisio autonomica systematis nervosi peripherici The autonomic nervous system (ANS or visceral nervous syste … Wikipedia
autonomic nervous system — n. the part of the nervous system that is responsible for control and regulation of the involuntary bodily functions, including those of the heart, blood vessels, visceral smooth muscles, and glands: it consists of the sympathetic system which,… … English World dictionary
autonomic nervous system — the system of nerves and ganglia that innervates the blood vessels, heart, smooth muscles, viscera, and glands and controls their involuntary functions, consisting of sympathetic and parasympathetic portions. [1895 1900] * * * Part of the nervous … Universalium
autonomic nervous system — ANS. The part of the nervous system that controls muscles of internal organs (such as the heart, blood vessels, lungs, stomach, and intestines) and glands (such as salivary glands and sweat glands). One part of the autonomic nervous system helps… … English dictionary of cancer terms
autonomic nervous system — noun the part of the nervous system of vertebrates that controls involuntary actions of the smooth muscles and heart and glands • Syn: ↑ANS • Hypernyms: ↑neural structure • Part Holonyms: ↑nervous system, ↑systema nervosum … Useful english dictionary
autonomic nervous system — the part of the peripheral nervous system responsible for the control of involuntary muscles (e.g. the heart, bladder, bowels) and hence those bodily functions that are not consciously directed, including regular beating of the heart, intestinal… … Medical dictionary
autonomic nervous system — the part of the peripheral nervous system responsible for the control of involuntary muscles (e.g. the heart, bladder, bowels) and hence those bodily functions that are not consciously directed, including regular beating of the heart, intestinal… … The new mediacal dictionary
autonomic nervous system — noun Date: 1898 a part of the vertebrate nervous system that innervates smooth and cardiac muscle and glandular tissues and governs involuntary actions (as secretion and peristalsis) and that consists of the sympathetic nervous system and the… … New Collegiate Dictionary
autonomic nervous system — noun In humans and other vertebrates, the part of the nervous system that regulates the involuntary activity of the heart, intestines and glands. These activities include digestion, respiration, perspiration, metabolism, and the modulation of… … Wiktionary
autonomic nervous system — noun Physiology, Anatomy the part of the peripheral nervous system which controls the involuntary functions of the glands, blood vessels, the viscera, and the heart and smooth muscles. Compare somatic nervous system … Australian English dictionary