sympathetic nervous system

noun

Definition of sympathetic nervous system

: the part of the autonomic nervous system that contains chiefly adrenergic fibers and tends to depress secretion, decrease the tone and contractility of smooth muscle, and increase heart rate — compare parasympathetic nervous system

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Recent Examples of sympathetic nervous system from the Web

This produces a stress response in your body—specifically, your brain’s hypothalamus triggers your sympathetic nervous system to release norepinephrine (aka adrenaline) and cortisol (a stress hormone) to get you out of harm’s way.

— brittany risher, SELF, "This Is When to See a Mental Health Professional About Your Anxiety," 2 Feb. 2018
Your sympathetic nervous system, which causes blood vessels to narrow, is the source of this mechanism.

— zahra barnes, SELF, "Raynaud’s Disease: Why Your Hands and Feet Hurt So Badly When They’re Cold," 15 Dec. 2017
Most researchers agree that rest is a physiological state during which your innate fight-or-flight stress response, or sympathetic nervous system, subsides in favor of a more relaxed condition.

— brad stulberg, The Cut, "How to Actually Get Some Rest for Once," 4 Oct. 2017

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'sympathetic nervous system.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

First Known Use of sympathetic nervous system

1850

in the meaning defined above

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Medical Dictionary

sympathetic nervous system

noun

medical Definition of sympathetic nervous system

: the part of the autonomic nervous system that is concerned especially with preparing the body to react to situations of stress or emergency, that contains chiefly adrenergic fibers and tends to depress secretion, decrease the tone and contractility of smooth muscle, increase heart rate, and that consists essentially of preganglionic fibers arising in the thoracic and upper lumbar parts of the spinal cord and passing through delicate white rami communicantes to ganglia located in a pair of sympathetic chains situated one on each side of the spinal column or to more peripheral ganglia or ganglionated plexuses and postganglionic fibers passing typically through gray rami communicantes to spinal nerves with which they are distributed to various end organs — called also sympathetic system; compare parasympathetic nervous system