autonomic nervous system

autonomic nervous system:

see nervous systemnervous system,
network of specialized tissue that controls actions and reactions of the body and its adjustment to the environment. Virtually all members of the animal kingdom have at least a rudimentary nervous system.
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Autonomic nervous system

The part of the nervous system that innervates smooth and cardiac muscle and the glands, and regulates visceral processes including those associated with cardiovascular activity, digestion, metabolism, and thermoregulation. The autonomic nervous system functions primarily at a subconscious level. It is traditionally partitioned into the sympathetic system and the parasympathetic system, based on the region of the brain or spinal cord in which the autonomic nerves have their origin. The sympathetic system is defined by the autonomic fibers that exit thoracic and lumbar segments of the spinal cord. The parasympathetic system is defined by the autonomic fibers that either exit the brainstem via the cranial nerves or exit the sacral segments of the spinal cord. See Parasympathetic nervous system, Sympathetic nervous system

The defining features of the autonomic nervous system were initially limited to motor fibers innervating glands and smooth and cardiac muscle. This definition limited the autonomic nervous system to visceral efferent fibers and excluded the sensory fibers that accompany most visceral motor fibers. Although the definition is often expanded to include both peripheral and central structures (such as the hypothalamus), contemporary literature continues to define the autonomic nervous system solely as a motor system. However, from a functional perspective, the autonomic nervous system includes afferent pathways conveying information regarding the visceral organs and the brain areas (such as the medulla and the hypothalamus) that interpret the afferent feedback and exert control over the motor output back to the visceral organs. See Homeostasis

Autonomic Nervous System

(also vegetative nervous system), the part of the nervous system that regulates the organs of blood circulation, respiration, digestion, excretion, and reproduction, as well as metabolism, thereby regulating the functional state of all the tissues of vertebrate animals and man.

The term “vegetative nervous system” was introduced by the French biologist M. Bichat (1800), who divided the nervous system into animal (somatic), that is, regulating the functions peculiar to animals alone and responsible for sensations and body movements, and vegetative, regulating the main vital processes—nutrition, respiration, reproduction, and growth (peculiar not only to animals but to plants as well). The functions regulated by the vegetative nervous system may not be performed or halted voluntarily. Hence the English physiologist J. Langley called it autonomic. However, the “autonomy” of the autonomic nervous system with respect to the higher divisions of the brain is extremely relative because impulses traveling from the cortex of the cerebral hemispheres to the centers of the autonomic nervous system may alter the functioning of the internal organs. Each complex reaction of the organism, any behavioral act, voluntary or involuntary, includes the sensing of stimuli, sensations, body movements, and the functional changes in the organs innervated by the autonomic nervous system.

The autonomic nervous system is divided into two parts according to anatomical and physiological features: sympathetic and parasympathetic. The centers of the sympathetic nervous system (SNS) are located in the thoracic and lumbar segments of the spinal cord. The centers of the parasympathetic nervous system (PNS) are located in the midbrain and medulla oblongata and in the sacral segments of the spinal cord. The main nerve of the PNS—the one that transmits the influence of the PNS to many organs of the body—is the vagus nerve. The sympathetic and parasympathetic centers are subordinated to the centers of the autonomic nervous system located in the diencephalon—in the hypothalamus, which coordinates the functions of both parts of the autonomic nervous system and regulates metabolism and the functions of many organs and systems. The highest control over the autonomic nervous system is exerted by the centers of the cerebral hemispheres that ensure the integrated reaction of the body and maintain through the autonomic nervous system the necessary correspondence of intensity between the vital processes—metabolism, blood circulation, respiration, and so on—and the requirements of the body.

All the sympathetic and parasympathetic nervous pathways to the periphery are formed by two successively connected nerve cells (neurons). The cell body of the first neuron is in the midbrain, medulla oblongata, or spinal cord. The long process (axon) of the first neuron ends in nerve cells on the periphery that form ganglia. Within the ganglion is the cell body of the second neuron, whose process transmits impulses to the organ it innervates. (The fibers of the first neuron are called preganglionic; the fibers of the second are called postganglionic.) Thus, the nerves of the autonomic nervous system, unlike the motor nerves of the striated muscles which are continuous after emerging from the central nervous system, have a break in their fibers. The peripheral neurons of the SNS form ganglia on both sides of the spinal cord (sympathetic trunks) and in the neck and abdominal cavity. The peripheral neurons of the PNS are located directly in the organs they innervate. Every preganglionic fiber ends in many neurons in the ganglia, which greatly widens the zone of influence of the preganglionic neurons. Every postganglionic neuron has endings formed by various processes of preganglionic neurons. Hence the impulses reaching the nerve cell via different nerve fibers may be summated.

The preganglionic nerve fibers have a thin medullated, or myelin, sheath and are 2-3½microns in diameter—that is, they are far thinner than the motor fibers innervating the striated muscles. Most of the postganglionic fibers lack a myelin sheath and are even thinner. The nerve fibers of the autonomic nervous system are characterized by low excitability and a low rate of conduction of excitation. The endings of the parasympathetic and sympathetic fibers differ with respect to the chemical transmitters of nervous impulses (mediators) formed in them. The mediator acetylcholine is formed in the endings of all the parasympathetic nerve fibers and the preganglionic sympathetic nerve fibers, as well as the postganglionic sympathetic fibers innervating the sweat glands. The mediator norepinephrine is formed in the endings of the postganglionic sympathetic fibers, except those innervating the sweat glands. The English physiologist H. Dale suggested dividing the nerve fibers into cholinergic and adrenergic ones, depending on the chemical nature of the mediators formed in their endings. After transection and degeneration of sympathetic or parasympathetic nerves, the sensitivity of the denervated organs to the corresponding mediators increases sharply. The organ deprived of sympathetic innervation is particularly sensitive to norepinephrine and epinephrine, while the organ deprived of parasympathetic innervation is particularly sensitive to acetylcholine.

Excitation of the SNS stimulates the body; excitation of the PNS helps to restore the resources used up by the body. The SNS and PNS are functional antagonists and therefore exert opposite influences on many organs. Thus, under the influence of impulses traveling along the sympathetic nerves, heart contractions accelerate and intensify, blood pressure in the arteries rises, glycogen is broken down in the liver and muscles, blood glucose increases, the pupils dilate, sensitivity of the sensory organs and efficiency of the central nervous system increase, the bronchi constrict, stomach and intestinal contractions are inhibited, the secretion of gastric and pancreatic juices diminishes, and the urinary bladder relaxes and evacuation is inhibited. Under the influence of impulses arriving via the parasympathetic nerves, heart contractions slow and weaken, arterial pressure drops, blood glucose decreases, stomach and intestinal contractions are stimulated, the secretion of gastric and pancreatic juices is intensified, and so on. The activity and state of certain organs are controlled solely by the sympathetic nerves—for example, the sweat glands, most blood vessels (except those of the tongue, salivary glands, and genitalia, the blood vessels of which are constricted by sympathetic nerves and dilated by parasympathetic nerves), adrenal glands, and uterus.

The autonomic nervous system has a threefold effect on organs: activating, correcting, and adaptotrophic. The activating effect is manifested by impulses stimulating the activity of an organ that functions periodically (for example, stimulation of secretion by the sweat glands under the influence of sympathetic nerves). The correcting effect is manifested by an intensification or weakening of the activity and state of excitation (tonus) of organs that possess automatism and that function continuously or are in a constant state of excitation (for example, the effect of the autonomic nervous system on heart action and the state of the blood vessels). The adaptotrophic function of the autonomic nervous system, mainly the SNS, consists of regulating metabolism and the functional state (excitability, efficiency) of organs and tissues; it prepares the body for activity and adjusts the work of the organs to external conditions and current needs of the body.

The role of the SNS in adapting the body to various situations requiring physical exertion was demonstrated in experiments on animals from whom both sympathetic trunks and all the sympathetic ganglia were removed (sympathectomy). While resting, such animals scarcely differ from normal ones. But during vigorous muscular exertion, overheating, chilling, loss of blood, or emotional stress, animals whose organs have been deprived of sympathetic influences have little endurance. Because of impairment of thermoregulation, they tolerate abrupt fluctuations in external temperature less easily than do normal animals. They become chilled sooner when exposed to cold and become overheated sooner when exposed to heat.

The autonomic nervous system (mainly its sympathetic division) becomes excited in extreme, life-threatening situations that require maximum exertion of the body’s forces—for example, suffocation, loss of blood, attack by an enemy, and trauma:—and in emotional reactions. This accounts for the acceleration and intensification of heart contractions, dilatation of the skin blood vessels, and reddening of the face in joy; for the pallor, sweating, gooseflesh, inhibition of gastric secretion, and change in intestinal peristalsis in fear; for pupil dilatation in anger, pain; and so on.

The physiological manifestations of emotions are caused mainly by excitation of the SNS. For example, in emotional stress and excitation of the central nervous system provoked by pain, impulses reaching certain endocrine glands along the fibers of the autonomic nervous system intensify the secretion of hormones into the blood. The American physiologist W. Cannon showed that emotional reactions increase the entry into the blood of epinephrine from the adrenal glands under the influence of impulses reaching them from the sympathetic nerves. Excitation of the autonomic centers of the hypothalamus resulting from pain stimulates the entry of various hormones from the pituitary, thyroid, and other glands into the blood. Release into the blood of epinephine (which affects many organs like the sympathetic nerves), vasopressin (which constricts the blood vessels and halts urination), and other hormones under the influence of the autonomic nervous system supplements and intensifies its direct action on the functions of various organs stimulated by the entry of nerve impulses. This is how neurohormonal regulation of the body’s activity is effected. Thus, the activity of the autonomic nervous system consists of the complementary interaction of its sympathetic and parasympathetic divisions. The SNS largely stimulates the processes associated with the release of energy (dissimilation), with activity, whereas the PNS stimulates the processes associated with the accumulation of energy and matter (assimilation).

REFERENCES

Gellhorn, E. Reguliatornye funktsii avtonomnoi nervnoi sistemy. Moscow, 1948. (Translated from English.)
Speranskaia, E. N. Voprosy fiziologii vegetativnogo otdela nervnoi sistemy. Moscow-Leningrad, 1961.
Rosin, Ia. A. Fiziologiia vegetativnoi nervnoi sistemy. Moscow, 1965.
Gellhorn, E., and G. Loofbourrow. Emotsii i emotsional’nye rasstroistva. Moscow, 1966. (Translated from English.)
Burn, J. H. The Autonomic Nervous System, 2nd ed. Oxford, 1965.
Triggle, D. J. Chemical Aspects of the Autonomic Nervous System. London-New York, 1965.
Botár, J. The Autonomic Nervous System. Budapest, 1966.
Gellhorn, E. Principles of Autonomic-Somatic Integrations. Minneapolis, 1967.

E. B. BABSKII

autonomic nervous system

[¦ȯd·ə¦näm·ik ′nər·vəs ‚sis·təm] (neuroscience) The visceral or involuntary division of the nervous system in vertebrates, which enervates glands, viscera, and smooth, cardiac, and some striated muscles.

Autonomic nervous system

autonomic

[aw″to-nom´ik] not subject to voluntary control.autonomic dysreflexia an uninhibited and exaggerated reflex of the autonomic nervous system" >autonomic nervous system to stimulation; called also hyperreflexia. The response occurs in 85 per cent of all patients who have spinal cord injury above the level of the sixth thoracic vertebra. It is potentially dangerous because of attendant vasoconstriction and immediate elevation of blood pressure, which in turn can bring about hemorrhagic retinal damage or stroke syndrome. Less serious effects include severe headache; changes in heart rate; sweating, flushing, and “goose bumps” or piloerection above the level of the spinal cord injury; and pallor below that level.Patient Care. Circumstances that can trigger autonomic dysreflexia are often related to stimulation of the bladder, bowel, and skin of the patient. Examples are a distended bowel or bladder, pressure on the skin, or any of a number of noxious stimuli.
Once the symptoms of autonomic dysreflexia are manifest, emergency care is indicated. Efforts are made to lower the blood pressure by placing the patient in a sitting position or elevating the head and upper body to a 45-degree angle. The stimulus must be identified and removed as gently and quickly as possible. If fecal impaction is the cause, the rectum should be coated with an anesthetic ointment prior to attempted removal of the impaction; this prevents increasing the stimulus to autonomic dysreflexia. The physician is notified so that appropriate medical intervention can be initiated. Antihypertensive drugs are a last resort. As soon as the cause is identified and removed, the dysreflexia will disappear. Patients who experience repeated attacks may require surgery to sever the nerves responsible for the exaggerated response to stimulation.autonomic nervous system the branch of the nervous system that works without conscious control. The voluntary nervous system governs the striated or skeletal muscles, whereas the autonomic nervous system governs the glands, cardiac muscle, and smooth muscles such as those of the digestive system, respiratory system, and skin. The autonomic nervous system is divided into two subsidiary systems, the sympathetic nervous system and the parasympathetic nervous system. See Plate 14.

system

[sis´tem] 1. a set or series of interconnected or interdependent parts or entities (objects, organs, or organisms) that act together in a common purpose or produce results impossible by action of one alone. 2. an organized set of principles or ideas. adj., adj systemat´ic, system´ic.
The parts of a system can be referred to as its elements or components; the environment of the system is defined as all of the factors that affect the system and are affected by it. A living system is capable of taking in matter, energy, and information from its environment (input), processing them in some way, and returning matter, energy, and information to its environment as output.
An open system is one in which there is an exchange of matter, energy, and information with the environment; in a closed system there is no such exchange. A living system cannot survive without this exchange, but in order to survive it must maintain pattern and organization in the midst of constant change. Control of self-regulation of an open system is achieved by dynamic interactions among its elements or components. The result of self-regulation is referred to as the steady state; that is, a state of equilibrium. homeostasis is an assemblage of organic regulations that act to maintain steady states of a living organism.
A system can be divided hierarchically into subsystems, which can be further subdivided into sub-subsystems and components. A system and its environment could be considered as a unified whole for purposes of study, or a subsystem could be studied as a system. For example, the collection of glands in the endocrine system can be thought of as a system, each endocrine gland could be viewed as a system, or even specific cells of a single gland could be studied as a system. It is also possible to think of the human body as a living system and the endocrine system as a subsystem. The division of a system into a subsystem and its environment is dependent on the perspective chosen by the person studying a particular phenomenon.

Systems, subsystems, and suprasystems. Within the environment there are suprasystems, such as human society, and systems within the suprasystem, such as the educational and industrial systems and the health care delivery system. Within the health care delivery system are subsystems, such as the patient, family members, the nurse, the physician, and allied health care professionals and paraprofessionals.alimentary system digestive system.apothecaries' system see apothecaries' system" >apothecaries' system.autonomic nervous system see autonomic nervous system.avoirdupois system see avoirdupois system" >avoirdupois system.behavioral system in the behavioral system model of nursing, the patterned, repetitive, and purposeful behaviors of an individual.cardiovascular system the heart and blood vessels, by which blood is pumped and circulated through the body; see also circulatory system.CD system (cluster designation) a system for classifying markers" >cell-surface markers expressed by lymphocytes based on a computer analysis of monoclonal antibodies against hla antigens, with antibodies having similar specificity characteristics being grouped together and assigned a number (CD1, CD2, CD3, etc.); these CD numbers are also applied to the specific antigens recognized by the various groups of monoclonal antibodies. See also antigen" >CD antigen.centimeter-gram-second system (CGS) (cgs) a system of measurements in which the units are based on the centimeter as the unit of length, the gram as the unit of mass, and the second as the unit of time.central nervous system see central nervous system.centrencephalic system the neurons in the central core of the brainstem from the thalamus to the medulla oblongata, connecting the hemispheres" >cerebral hemispheres.circulatory system see circulatory system.client system in the general systems framework and theory of goal attainment" >general systems framework and theory of goal attainment, the composite of physiological, psychological, sociocultural, and developmental variables that make up the total person.colloid system (colloidal system) colloid (def. 3).conduction system (conductive system (of heart)) the system of atypical cardiac muscle fibers, comprising the sinoatrial and atrioventricular nodes, internodal tracts, atrioventricular bundle, bundle branch, and terminal ramifications into the Purkinje network.digestive system see digestive system.Emergency Medical Services (EMS) system a comprehensive program designed to provide services to the patient in the prehospital setting. The system is activated when a call is made to the EMS operator, who then dispatches an ambulance to the patient. The patient receives critical interventions and is stabilized at the scene. A communication system allows the health care workers at the scene to contact a trauma center for information regarding further treatment and disposition of the patient, followed by transportation of the patient to the most appropriate facility for treatment.endocrine system the system of ductless glands and other structures that produce internal secretions (hormones) that are released directly into the circulatory system, influencing metabolism and other body processes; see endocrine glands.environmental control system unit" >environmental control unit.expert system a set of computer programs designed to serve as an aid in decision making.extrapyramidal system see extrapyramidal system.gateway system a software interface between an online searcher and one or more search systems, facilitating the use of the system by searchers who are unfamiliar with it, or with online retrieval in general.genitourinary system the organs concerned with production and excretion of urine, together with the reproductive organs. (See Plates.) Called also urogenital system.haversian system a canal" >haversian canal and its concentrically arranged lamellae, constituting the basic unit of structure in compact bone (osteon).

Haversian system: Structures of compact and spongy bone with the central haversian canal surrounded by the lamellae. From Applegate, 2000.health care system see health care system.heterogeneous system a system or structure made up of mechanically separable parts, as an emulsion or suspension.His-Purkinje system the intraventricular conduction system from the bundle of His to the distal Purkinje fibers, which carries the impulse to the ventricles.Home Health Care Classification system see home health care classification system.homogeneous system a system or structure made up of parts that cannot be mechanically separated, as a solution.hypophyseoportal system (hypophysioportal system) (hypothalamo-hypophysial portal system) the venules connecting the hypothalamus with the sinusoidal capillaries of the anterior lobe of the pituitary gland; they carry releasing substances to the pituitary.immune system see immune system.interpersonal system in the general systems framework and theory of goal attainment, two or more individuals interacting in a given situation.lay health system a system comprising an informal referral network and sources of treatment outside the formal biomedical sources of health care; it includes individual consultation and information-seeking through significant others and peers concerning health behaviors, symptoms, and evaluation of treatment before, during, and after consultation with health care professionals.legal system in the omaha system, anything connected with law or its administration; it includes legal aid, attorney, courts, or Child Protective Services (CPS), and many other agencies and officials.limbic system a system of brain structures common to the brains of all mammals, comprising the phylogenetically old cortex (archipallium and paleopallium) and its primarily related nuclei. It is associated with olfaction, autonomic functions, and certain aspects of emotion and behavior.lymphatic system see lymphatic system.lymphoid system the lymphoid tissue of the body, collectively; it consists of primary (or central) lymphoid tissues, the bone marrow, and thymus, and secondary (or peripheral) tissues, the lymph nodes, spleen, and gut-associated lymphoid tissue (tonsils, Peyer's patches).lymphoreticular system the lymphoid and reticuloendothelial systems considered together; see also lymphoreticular disorders.metric system see metric system.mononuclear phagocyte system the group of highly phagocytic cells that have a common origin from stem cells of the bone marrow and develop circulating monocytes and tissue macrophages, which develop from monocytes that have migrated to connective tissue of the liver (kupffer's cells), lung, spleen, and lymph nodes. The term has been proposed to replace reticuloendothelial system, which includes some cells of different origin and does not include all macrophages.nervous system see nervous system.nursing system in the self-care model of nursing, all the actions and interactions of nurses and patients in nursing practice situations; nursing systems fall into three categories: wholly compensatory, partly compensatory, and supportive-educative.Omaha system see omaha system.oxygen delivery system a device that delivers oxygen through the upper airways to the lungs at concentrations above that of ambient air. There are two general types: the fixed performance or high flow type, which can supply all of the needs of a patient for inspired gas at a given fractional inspired oxygen; and the variable performance or low flow type, which cannot supply all of the patient's needs for oxygen and delivers fractional inspired oxygen that varies with ventilatory demand.parasympathetic nervous system see parasympathetic nervous system" >parasympathetic nervous system.peripheral nervous system the portion of the nervous system consisting of the nerves and ganglia outside the brain and spinal cord.personal system in the general systems framework and theory of goal attainment, the unified self, a complex whole that is rational, conscious, and feeling and that sets goals and decides on the means of achieving them.pituitary portal system hypothalamo-hypophysial portal system.portal system an arrangement by which blood collected from one set of capillaries passes through a large vessel or vessels and another set of capillaries before returning to the systemic circulation, as in the pituitary gland (the hypothalamo-hypophysial portal system) or the liver (the hepatic portal circulation).renin-angiotensin-aldosterone system see renin-angiotensin-aldosterone system.respiratory system the group of specialized organs whose specific function is to provide for the transfer of oxygen from the air to the blood and of waste carbon dioxide from the blood to the air. The organs of the system include the nose, the pharynx, the larynx, the trachea, the bronchi, and the lungs. See also respiration and Plates 7 and 8.reticular activating system see reticular activating system.reticuloendothelial system see reticuloendothelial system.safety system see safety system." >safety system.SI system see SI units.skeletal system see skeletal system.social system in the general systems framework and theory of goal attainment, an organized boundary system of social roles, behaviors, and practices developed to maintain balance for growth, development, and performance, which involves an exchange of energy and information between the person and the environment for regulation and control of stressors.support system in the omaha system, the circle of friends, family, and associates that provide love, care, and need gratification; it may include church, school, workplace, or other groupings.sympathetic nervous system see sympathetic nervous system.Unified Medical Language system see unified medical language system.Unified Nursing Language system see unified nursing language system.unit dose system a method of delivery of patient medications directly to the patient care unit. Following review by a nurse, a copy of the physician's original order is sent to the pharmacy, where the pharmacist reviews it again. The pharmacist then fills the order and delivers the medication to the patient care unit, usually in a 24-hour supply. Each patient has an individual supply of medications prepared and labeled by the pharmacist.urinary system the system formed in the body by the kidneys, ureters, urinary bladder, and urethra, the organs concerned in the production and excretion of urine.urogenital system genitourinary system.vascular system circulatory system.vasomotor system the part of the nervous system that controls the caliber of the blood vessels.

autonomic (visceral motor) division of nervous system

[TA] that part of the nervous system that represents the motor innervation of smooth muscle, cardiac muscle, and gland cells. It consists of two physiologically and anatomically distinct, mutually antagonistic components: the sympathetic and parasympathetic parts. In both these parts, the pathway of innervation consists of a synaptic sequence of two motor neurons, one of which lies in the spinal cord or brainstem as the presynaptic (also called preganglionic or B fiber) neuron, the thin but myelinated axon of which emerges with an outgoing spinal or cranial nerve and synapses with one or more of the postsynaptic (postganglionic or, more strictly, ganglionic) neurons composing the autonomic ganglia; the unmyelinated postsynaptic fibers in turn innervate the smooth muscle, cardiac muscle, or gland cells. The presynaptic neurons of the sympathetic part lie in the intermediolateral cell column of the thoracic and upper two lumbar segments of the spinal gray matter; those of the parasympathetic part compose the visceral motor (visceral efferent) nuclei of the brainstem as well as the lateral column of the second to fourth sacral segments of the spinal cord. The ganglia of the sympathetic part are the paravertebral ganglia of the sympathetic trunk and the lumbar and sacral prevertebral or collateral ganglia; those of the parasympathetic part lie either near the organ to be innervated or as intramural ganglia within the organ itself except in the head, where there are four discrete parasympathetic ganglia (ciliary, otic, pterygopalatine, and submandibular). Impulse transmission from presynaptic to postsynaptic neuron is mediated by acetylcholine in both the sympathetic and parasympathetic parts; transmission from the postsynaptic fiber to the visceral effector tissues is classically said to be by acetylcholine in the parasympathetic part and by noradrenalin in the sympathetic part; recent evidence suggests the existence of further noncholinergic, nonadrenergic classes of postsynaptic fibers. Synonym(s): divisio autonomica systematis nervosi peripherici [TA], pars autonomica systematis nervosi peripherici [TA], autonomic part of peripheral nervous system ☆ , autonomic nervous system, involuntary nervous system, systema nervosum autonomicum, vegetative nervous system, visceral motor system, visceral nervous system

autonomic nervous system

n. The part of the vertebrate nervous system that regulates involuntary action, as of the intestines, heart, and glands, and that is divided into the sympathetic nervous system and the parasympathetic nervous system.

au·to·no·mic di·vi·sion of ner·vous sys·tem

(aw'tō-nom'ik di-vizh'ŭn nĕr'vŭs sis'tĕm) That part of the nervous system that represents the motor innervation of smooth muscle, cardiac muscle, and gland cells. It consists of two physiologically and anatomically distinct, mutually antagonistic components: the sympathetic and parasympathetic parts. In both of these parts the pathway of innervation consists of a synaptic sequence of two motor neurons, one of which lies in the spinal cord or brainstem as the presynaptic (preganglionic) neuron, the thin but myelinated axon of which (preganglionic [presynaptic] or B fiber) emerges with an outgoing spinal or cranial nerve and synapses with one or more of the postsynaptic (postganglionic or, more strictly, ganglionic) neurons comprising the autonomic ganglia; theunmyelinated postsynaptic fibers in turn innervate the smooth muscle, cardiac muscle, or gland cells. The presynaptic neurons of the sympathetic part lie in the intermediolateral cell column of the thoracic and upper two lumbar segments of the spinal gray matter; those of the parasympathetic part comprise the visceral motor (visceral efferent) nuclei of the brainstem as well as the lateral column of the second to fourth sacral segments of the spinal cord. The ganglia of the sympathetic part are the paravertebral ganglia of the sympathetic trunk and the lumbar and sacral prevertebral or collateral ganglia; those of the parasympathetic part lie either near the organ to be innervated or as intramural ganglia within the organ itself except in the head, where there are four discrete parasympathetic ganglia (ciliary, otic, pterygopalatine, and submandibular). Impulse transmission from presynaptic to postsynaptic neuron is mediated by acetylcholine in both the sympathetic and parasympathetic parts; transmission from the postsynaptic fiber to the visceral effector tissues is classically said to be by acetylcholine in the parasympathetic part and by noradrenalin in the sympathetic part; recent evidence suggests the existence of further noncholinergic, nonadrenergic classes of postsynaptic fibers.
Synonym(s): divisio autonomica systematis nervosi peripherici [TA] , autonomic nervous system.

autonomic nervous system

ANS

AUTONOMIC NERVOUS SYSTEMThe parts of the nervous system that control unconscious, involuntary, and visceral body functions. The autonomic nervous system reflexively balances the body's smooth muscle tone, blood pressure, temperature, fluid composition, state of digestion, metabolic activity, and sexual activation. In the central nervous system (CNS), the activities of the autonomic nervous system (ANS) are coordinated in the brainstem (especially in the nucleus of the tractus solitarius) and in the hypothalamus. In the peripheral nervous system (PNS), the ANS comprises the visceral motor axons, the visceral sensory axons, and the enteric nervous system (a neural net within the walls of the gastrointestinal tract). Compared to peripheral somatic axons, the peripheral autonomic axons tend to be small (less than 3 µm in diameter), slowly conducting, and sparsely myelinated. The autonomic motor circuits also differ from somatic motor pathways. Peripheral somatic motor pathways, i.e., the circuitry sending signals to skeletal muscles, are only one axon long; axons of somatic motor neurons in the spinal cord and brainstem synapse directly on the effector cell, a muscle cell. In contrast, peripheral autonomic motor pathways are two axons long. First, an axon (a preganglionic axon) of a visceral motor neuron in the spinal cord or brainstem synapses on a neuron in a peripheral ganglion. Second, the axon (a postganglionic axon) of the ganglion neuron synapses on the effector cell, a smooth muscle cell, a cardiac muscle cell, or a secretory cell.

This autonomic motor circuitry is further subdivided into two parallel subsystems; the sympathetic and the parasympathetic. The subsystems differ in two major ways: 1. In the sympathetic system, the central (preganglionic) neurons are located only in the thoracic and lumbar segments of the spinal cord; in the parasympathetic system, the central neurons are located only in the brainstem and in a short segment of the caudal end of the spinal cord. 2. In the sympathetic system, norepinephrine is the characteristic neurotransmitter of the postganglionic axons; in the parasympathetic system, acetylcholine is the characteristic neurotransmitter of the postganglionic axons. In both the sympathetic and parasympathetic systems, the characteristic neurotransmitter of the preganglionic axons is acetylcholine.Besides their characteristic neurotransmitters, autonomic nerves influence surrounding tissues through the release of other active chemicals including ATP, nitric oxide, and a range of peptides, e.g., substance P and vasoactive intestinal peptide. As a result of their different final transmitters, the effects of the two subsystems differ. Sympathetic stimulation readies an animal for interaction with the outside world and prepares the animal for "fight or flight"; e.g., activation of sympathetic axons increases heart rate and decreases gastrointestinal peristalsis. On the other hand, parasympathetic stimulation relaxes and quiets an animal; e.g., activation of parasympathetic axons decreases heart rate and increases gastrointestinal peristalsis. The accompanying table compares the effects of sympathetic and parasympathetic stimulation on specific tissues. See: parasympathetic nervous system; sympathetic nervous system; illustrationtable

Pathology

The ANS is distributed throughout the body, and autonomic dysfunction can produce a wide range of symptoms, such as bladder malfunction, blood pressure abnormalities, breathing difficulty, gastrointestinal motility problems, heart arrhythmias, impotence, nasal congestion, sweating disorders, syncope, and visual symptoms. Drugs that act on or mimic autonomic neurotransmitters are commonly used to alleviate these symptoms as well as other conditions, such as glaucoma, heart failure, shock, and thyroid storm. To assess the overall functioning of the ANS, physicians often begin with simple measurements of the reflexive responses of the cardiovascular system; specifically, they measure the changes of blood pressure and heart rate as a person stands from sitting and exercises.

Tissue:	Effects:
	Sympathetic Stimulation	Parasympathetic Stimulation
adipose tissue	lipolysis
adrenal cortex
secretion (corticoids)	increase
adrenal medulla
secretion (adrenaline)	increase
arteries
abdominal organs	constriction
coronary	dilation
skin and mucosa	constriction
bladder
wall (detrusor) muscle	relaxation	contraction
sphincter	contraction	relaxation
gall bladder
wall muscle	relaxation	contraction
duct	dilation	constriction
heart
AV node (conduction velocity)	increase	decrease
SA node (rate)	increase	decrease
atrial muscle (contractility)	increase	decrease
ventricular muscle (contractility)	increase
intestine
wall muscle (tone and motility)	decrease	increase
secretion	decrease	increase
rectal sphincter muscle	contraction	relaxation
kidney
secretion (renin)	increase
lacrimal gland
secretion (tears)		increase
liver
metabolism	glycogenolysis, gluconeogenesis	glycogen synthesis
bile secretion	decrease	increase
lung
airways	dilation	constriction
secretion (airway glands)		increase
nasopharynx
secretion (mucosal glands)		increase
pancreas
secretion (enzymes and insulin)	decrease	increase
secretion (glucagon)	increase
pineal gland
melatonin synthesis	stimulation
pupil	dilation	constriction
reproductive tract
muscles	contractions
blood vessels	constriction	dilation, erection
salivary gland
secretion	decrease	increase
skeletal muscle	increase contractility, glycogenolysis
skin
pilomotor muscle	contraction
secretion (sweat)	increase
spleen
capsule	contraction
stomach
wall muscle (tone and motility)	decrease	increase
secretion	decrease	increase
uterus
pregnant	contraction
nonpregnant	relaxation

autonomic nervous system

The part of the nervous system controlling involuntary functions, such as the heart beat, the secretion of glands and the contraction of blood vessels. It is subdivided into the SYMPATHETIC and the PARASYMPATHETIC divisions which are, in general, antagonistic and in balance. The term autonomic derives from the Greek autos , self, and nomos , a law.

autonomic nervous system

the part of the nervous system that controls the involuntary activities of the body There are two main parts:

The sympathetic nervous system., in which complexes of SYNAPSES form ganglia alongside the vertebrae, and the preganglionic fibres from the central nervous system are therefore short; the fibres are ADRENERGIC. (b) The parasympathetic nervous system, in which the ganglia are embedded in the wall of the effector so that the preganglionic fibres are long and the postganglionic fibres short; these are CHOLINERGIC.

sympathetic system inhibits peristalsis stimulates contraction in sphincters of bladder and anus inhibits bladder contraction stimulates pacemaker, speeding up heart stimulates arterial constriction inhibits contraction of bronchioles, causing dilation inhibits contraction of iris muscle, causing dilated pupil parasympathetic system stimulates peristalis inhibits contraction in sphincters of bladder and anus stimulates bladder contraction inhibits pacemaker, slowing down heart inhibits arterial constriction, causing dilation stimulates contraction of bronchioles stimulates contraction of iris muscle, causing reduced pupil.

The sympathetic and parasympathetic systems innervate the same end organs, but the effects produced by the two systems generally oppose one another, for example:

Autonomic nervous system (ANS)

The part of the nervous system that supplies nerve endings in the blood vessels, heart, intestines, glands, and smooth muscles, and governs their involuntary functioning. The autonomic nervous system is responsible for the biochemical changes involved in experiences of anxiety.Mentioned in: Anxiety, Biofeedback, Dizziness, Guided Imagery, Shy-Drager Syndrome, Spinal Cord Injury

au·to·nom·ic

(aw'tō-nom'ik) Relating to the autonomic nervous system.

autonomic nervous system

autonomic nervous system

autonomic nervous system

au′tonom′ic nerv′ous sys`tem

au·to·nom·ic nervous system

autonomic nervous system

autonomic nervous system

autonomic nervous system:

Autonomic nervous system

Autonomic Nervous System

REFERENCES

autonomic nervous system

Autonomic nervous system

autonomic

system

autonomic (visceral motor) division of nervous system

autonomic nervous system

au·to·no·mic di·vi·sion of ner·vous sys·tem

autonomic nervous system

ANS

Pathology

autonomic nervous system

autonomic nervous system

Autonomic nervous system (ANS)

au·to·nom·ic

autonomic nervous system

Synonyms for autonomic nervous system

noun the part of the nervous system of vertebrates that controls involuntary actions of the smooth muscles and heart and glands

Synonyms

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