Table of ContentsView AllTable of ContentsFunctionAnatomyHow it Works
Table of ContentsView All
View All
Table of Contents
Function
Anatomy
How it Works
The sympatheticnervous system(SNS) is responsible forthe body’s stress responseand is activated when you perceive danger.The brain sends messages to the rest of the body to prepare for and respond to danger, initiating a fight, flight, freeze, or fawn stress response. If the SNS is chronically activated, it can impact your health.
Learn about the sympathetic nervous system function and your body’s response to perceived danger.
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Function of the Sympathetic Nervous System
The primary function of the sympathetic nervous system is to keep your body safe from danger.When you perceive a threat, your sympathetic nervous system helps prepare your body and mind for impending danger.This is known as a stress response.
Types of Stress Responses
Scientists initially categorized thestress responseas a fight or flight response.More recently, two more reactions have been identified: Freeze or fawn.Sympathetic nervous system stress responses include:
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Sympathetic Nervous System Anatomy
The two main parts of the sympathetic nervous system are thebrainand thespinal cord.
Once the brain is alerted to a threat, it sends messages vianeurons(chemical messengers) to clusters of nerve cells calledganglia, which are responsible for sensory and motor responses. Then, the ganglia send those neurons to the body parts that respond to danger, such as muscles needed to run away or fight.
Sympathetic vs. Parasympathetic Nervous System (PNS)
How the Sympathetic Nervous System Works
When the brain senses danger, theamygdala, responsible for interpreting external stimuli, sends a message to thehypothalamus, which is responsible for maintaining our body’s baseline state.Then the brain releaseshormonesthat cause the body to react.
What Happens When the Sympathetic Nervous System Is Activated?
Some other parts of your body that respond when the sympathetic nervous system is activated include:
Sometimes the sympathetic nervous system becomes activated when there is no real danger or remains activated after the threat is gone.Long-term activation of the sympathetic nervous system has been linked to health concerns such as:
It can also lead to physical effects such asfatigue.
Summary
The sympathetic nervous system helps to protect you from danger. When you perceive danger, your brain and spinal cord release chemicals and send messages to other body parts to respond. Physical changes take place to make the body and mind more able to respond to the threat. The parasympathetic nervous system creates an opposite response after the threat is gone, which allows the body and mind to rest and recover.
16 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.American Psychological Association.Sympathetic nervous system.American Psychological Association.Stress effects on the body.Encyclopedia Britannica.Sympathetic nervous system.Simple Psychology.Fight, flight, freeze, or fawn: what this response means.Encyclopedia Britannica.Fight-or-flight response.Zingela Z, Stroud L, Cronje J, Fink M, van Wyk S.The psychological and subjective experience of catatonia: a qualitative study.BMC Psychol. 2022;10(1):173. doi:10.1186/s40359-022-00885-7American Psychological Association.Fight-or-flight response.American Psychological Association.Autonomic nervous system (ANS).Hospital for Special Surgery.How the parasympathetic nervous system can lower stress.American Psychological Association.Parasympathetic nervous system.Harvard Medical School.Understanding the stress response.Endocrine Society.Adrenal hormones.The American Institute of Stress.How stress affects your vision.DeLalio LJ, Sved AF, Stocker SD.Sympathetic nervous system contributions to hypertension: updates and therapeutic relevance.Canadian Journal of Cardiology. 2020;36(5):712-720. doi:10.1016/j.cjca.2020.03.003Harvard Medical School.Stress and the sensitive gut.Won E, Kim YK.Stress, the autonomic nervous system, and the immune-kynurenine pathway in the etiology of depression.Curr Neuropharmacol. 2016;14(7):665-673. doi:10.2174/1570159X14666151208113006
16 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.American Psychological Association.Sympathetic nervous system.American Psychological Association.Stress effects on the body.Encyclopedia Britannica.Sympathetic nervous system.Simple Psychology.Fight, flight, freeze, or fawn: what this response means.Encyclopedia Britannica.Fight-or-flight response.Zingela Z, Stroud L, Cronje J, Fink M, van Wyk S.The psychological and subjective experience of catatonia: a qualitative study.BMC Psychol. 2022;10(1):173. doi:10.1186/s40359-022-00885-7American Psychological Association.Fight-or-flight response.American Psychological Association.Autonomic nervous system (ANS).Hospital for Special Surgery.How the parasympathetic nervous system can lower stress.American Psychological Association.Parasympathetic nervous system.Harvard Medical School.Understanding the stress response.Endocrine Society.Adrenal hormones.The American Institute of Stress.How stress affects your vision.DeLalio LJ, Sved AF, Stocker SD.Sympathetic nervous system contributions to hypertension: updates and therapeutic relevance.Canadian Journal of Cardiology. 2020;36(5):712-720. doi:10.1016/j.cjca.2020.03.003Harvard Medical School.Stress and the sensitive gut.Won E, Kim YK.Stress, the autonomic nervous system, and the immune-kynurenine pathway in the etiology of depression.Curr Neuropharmacol. 2016;14(7):665-673. doi:10.2174/1570159X14666151208113006
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
American Psychological Association.Sympathetic nervous system.American Psychological Association.Stress effects on the body.Encyclopedia Britannica.Sympathetic nervous system.Simple Psychology.Fight, flight, freeze, or fawn: what this response means.Encyclopedia Britannica.Fight-or-flight response.Zingela Z, Stroud L, Cronje J, Fink M, van Wyk S.The psychological and subjective experience of catatonia: a qualitative study.BMC Psychol. 2022;10(1):173. doi:10.1186/s40359-022-00885-7American Psychological Association.Fight-or-flight response.American Psychological Association.Autonomic nervous system (ANS).Hospital for Special Surgery.How the parasympathetic nervous system can lower stress.American Psychological Association.Parasympathetic nervous system.Harvard Medical School.Understanding the stress response.Endocrine Society.Adrenal hormones.The American Institute of Stress.How stress affects your vision.DeLalio LJ, Sved AF, Stocker SD.Sympathetic nervous system contributions to hypertension: updates and therapeutic relevance.Canadian Journal of Cardiology. 2020;36(5):712-720. doi:10.1016/j.cjca.2020.03.003Harvard Medical School.Stress and the sensitive gut.Won E, Kim YK.Stress, the autonomic nervous system, and the immune-kynurenine pathway in the etiology of depression.Curr Neuropharmacol. 2016;14(7):665-673. doi:10.2174/1570159X14666151208113006
American Psychological Association.Sympathetic nervous system.
American Psychological Association.Stress effects on the body.
Encyclopedia Britannica.Sympathetic nervous system.
Simple Psychology.Fight, flight, freeze, or fawn: what this response means.
Encyclopedia Britannica.Fight-or-flight response.
Zingela Z, Stroud L, Cronje J, Fink M, van Wyk S.The psychological and subjective experience of catatonia: a qualitative study.BMC Psychol. 2022;10(1):173. doi:10.1186/s40359-022-00885-7
American Psychological Association.Fight-or-flight response.
American Psychological Association.Autonomic nervous system (ANS).
Hospital for Special Surgery.How the parasympathetic nervous system can lower stress.
American Psychological Association.Parasympathetic nervous system.
Harvard Medical School.Understanding the stress response.
Endocrine Society.Adrenal hormones.
The American Institute of Stress.How stress affects your vision.
DeLalio LJ, Sved AF, Stocker SD.Sympathetic nervous system contributions to hypertension: updates and therapeutic relevance.Canadian Journal of Cardiology. 2020;36(5):712-720. doi:10.1016/j.cjca.2020.03.003
Harvard Medical School.Stress and the sensitive gut.
Won E, Kim YK.Stress, the autonomic nervous system, and the immune-kynurenine pathway in the etiology of depression.Curr Neuropharmacol. 2016;14(7):665-673. doi:10.2174/1570159X14666151208113006
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