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ANS

Abbreviation for autonomic nervous system.

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American Nimodipine Study. A clinical trial that assessed nimodipine’s effect on mortality in post-acute stroke patients.
Conclusions Nimodipine has no effect on patients at 48 hours, but may be beneficial at 18 hours.

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Abbreviation for autonomic nervous system.

autonomic nervous system

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AUTONOMIC NERVOUS SYSTEM
The 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 StimulationParasympathetic Stimulation
adipose tissuelipolysis
adrenal cortex
secretion (corticoids)increase
adrenal medulla
secretion (adrenaline)increase
arteries
abdominal organsconstriction
coronarydilation
skin and mucosaconstriction
bladder
wall (detrusor) musclerelaxationcontraction
sphinctercontractionrelaxation
gall bladder
wall musclerelaxationcontraction
ductdilationconstriction
heart
AV node (conduction velocity)increasedecrease
SA node (rate)increasedecrease
atrial muscle (contractility)increasedecrease
ventricular muscle (contractility)increase
intestine
wall muscle (tone and motility)decreaseincrease
secretiondecreaseincrease
rectal sphincter musclecontractionrelaxation
kidney
secretion (renin)increase
lacrimal gland
secretion (tears)increase
liver
metabolismglycogenolysis, gluconeogenesisglycogen synthesis
bile secretiondecreaseincrease
lung
airwaysdilationconstriction
secretion (airway glands)increase
nasopharynx
secretion (mucosal glands)increase
pancreas
secretion (enzymes and insulin)decreaseincrease
secretion (glucagon)increase
pineal gland
melatonin synthesisstimulation
pupildilationconstriction
reproductive tract
musclescontractions
blood vesselsconstrictiondilation, erection
salivary gland
secretiondecreaseincrease
skeletal muscleincrease contractility, glycogenolysis
skin
pilomotor musclecontraction
secretion (sweat)increase
spleen
capsulecontraction
stomach
wall muscle (tone and motility)decreaseincrease
secretiondecreaseincrease
uterus
pregnantcontraction
nonpregnantrelaxation

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

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autonomic nervous system

autonomic nervous system

; ANS the involuntary nervous system regulating systemic function and blood flow; under overall hypothalamic control and inputting to homeostatic mechanisms; divided into sympathetic and parasympathetic divisions

ANS

Abbreviation for autonomic nervous system.
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