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Physical
Sympathetic Nervous System
The sympathetic nervous system is the part of the autonomic nervous system that triggers the body's fight-or-flight response.
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The idea
Your body runs many jobs without you thinking about them, such as your heartbeat and digestion. The autonomic nervous system controls these jobs, and the sympathetic nervous system is one of its three divisions. The other two are the parasympathetic nervous system and the enteric nervous system.
The main job of the sympathetic system is to start the fight-or-flight response. When you face danger, it gets your body ready to act quickly, for example by making your heart pump harder. It is not only for emergencies, though. It stays active at a low level all the time to help keep the body's conditions steady, a balance called homeostasis.
The sympathetic system works against the parasympathetic system, which helps the body rest and digest. Together they act like an accelerator and a brake. The sympathetic system also plays a part in blood sugar levels, body temperature and the immune system. When it does not work properly, it has been linked to a range of health problems.
Check yourself
Question 1 of 2
Which response does the sympathetic nervous system mainly trigger?
Composition
what it's made of
- Sympathetic neurons — Nerve cells of the system, which first form before birth and keep changing with age.
- Fight-or-flight trigger — Its primary job: preparing the body to react to danger.
- Baseline activity — A constant low level of activity that helps maintain homeostasis.
- Body controls — Influence over blood sugar, body temperature, heart output and immune function.
Connection
how it relates
Under Autonomic Nervous System
Change
how and why it evolves
- Past
- Sympathetic neurons first form before birth, at the embryo stage of life.
- Now
- The system keeps developing as a person ages, and scientists study how its changes are linked to health and disease.
- Next
- Better understanding of the sympathetic system may help doctors treat stress-related and heart conditions, though much of this work is still in progress.