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Physical
Parasympathetic Nervous System
The parasympathetic nervous system is the rest-and-digest part of the autonomic nervous system that calms the body.
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The idea
The parasympathetic nervous system is one of three divisions of the autonomic nervous system, which runs the body's automatic actions. The other two divisions are the sympathetic and the enteric nervous systems. It is often called the "rest-and-digest" system because it is most active when the body is at rest, especially after eating.
It triggers activities such as making saliva and tears, digesting food, and emptying the bladder. Its work balances the sympathetic nervous system, which drives the fight-or-flight response. While the sympathetic side takes over during sudden stress, the parasympathetic side helps the body save energy, store fuel and keep a steady inner balance called homeostasis.
Its nerve fibers start in the central nervous system, the brain and spinal cord. They travel in several cranial nerves, including the vagus nerve, and in three spinal nerves in the sacrum, near the base of the spine. The vagus nerve links the brain to the heart, lungs and digestive tract, and it helps lower the heart rate and calm the body after stress. Because its nerves leave from the skull and the sacrum, scientists say it has a "craniosacral outflow".
Check yourself
Question 1 of 3
Which scientist, who coined the term autonomic nervous system, named the parasympathetic nervous system as one of its divisions?
Composition
what it's made of
- Vagus nerve — The main parasympathetic nerve, linking the brain to the heart, lungs and digestive tract.
- Other cranial nerves — The oculomotor, facial and glossopharyngeal nerves also carry parasympathetic fibers.
- Pelvic splanchnic nerves — Three spinal nerves from the sacrum that act as parasympathetic nerves.
- Rest-and-digest actions — Saliva, tears, digestion and urination, which happen when the body is at rest.
Connection
how it relates
Under Autonomic Nervous System
Change
how and why it evolves
- Past
- The scientist John Newport Langley, who coined the term autonomic nervous system in 1898, named the parasympathetic nervous system as one of its divisions. The vagus nerve was once called the pneumogastric nerve, a name that reflected its role in both the lungs and the digestive system. A 2016 study in mice suggested that the sacral nerves may really belong to the sympathetic system, but later analyses argued that they should still be classed as parasympathetic.
- Now
- Today researchers and doctors use heart rate variability, the small changes in time between heartbeats, as a sign of how active the parasympathetic system is.
- Next
- Scientists have found that signals in the vagus nerve can help damp down inflammation. This finding may lead to new treatments for some immune and inflammatory diseases.