Parasympathetic nervous system
Say it: pair-uh-sim-puh-THET-ik NUR-vus SIS-tum
The parasympathetic nervous system is the autonomic division that conserves energy and controls rest-and-digest activities such as digestion.
Also: parasympathetic division, craniosacral division
Definition
What is the parasympathetic nervous system?
The parasympathetic nervous system is the second main division of the autonomic nervous system. Its first neurons sit in nuclei of the brainstem and in the sacral part of the spinal cord, so it is also called the craniosacral division. Their axons leave through four cranial nerves, the oculomotor, facial, glossopharyngeal and vagus nerves, and through sacral spinal nerves. Unlike sympathetic fibers, these preganglionic axons are long and end in terminal ganglia lying next to, or inside the wall of, the organ they control, so the second neurons are short.
Parasympathetic activity slows the heart, narrows the pupils and airways, increases the flow of saliva and tears, stimulates gut movement and digestive secretions, and helps empty the bladder. The vagus nerve carries most of this output to the heart, lungs and abdominal organs. Both the preganglionic and the postganglionic neurons release acetylcholine, which acts on nicotinic receptors in the ganglia and mainly on muscarinic receptors in the target tissues.
Most organs receive both divisions, and their opposing effects keep functions such as heart rate in balance. Drugs that block muscarinic receptors, such as atropine, speed the heart and dry the mouth, while drugs that mimic acetylcholine are used for some eye and bladder conditions.
Word parts
Where does the term “parasympathetic nervous system” come from?
- para-
- beside, alongsideGreek para
- sym-
- together, withGreek syn
- -pathetic
- feelingGreek pathos, via sympatheia
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Terms that go with it
- Autonomic nervous systemThe autonomic nervous system is the division of the nervous system that runs involuntary functions such as heart rate, digestion and gland secretion.
- Sympathetic nervous systemThe sympathetic nervous system is the division of the autonomic nervous system that readies the body for action, producing the fight-or-flight response.
- AcetylcholineAcetylcholine is the neurotransmitter motor neurons use to make skeletal muscles contract, and a key messenger in the autonomic nervous system and brain.
- HomeostasisHomeostasis is the body's ability to keep internal conditions, such as temperature, blood glucose and pH, steady while conditions around it change.
- DigestionDigestion is the process by which the body breaks food down, by chewing, churning and enzymes, into molecules small enough to absorb into the blood.
- HeartThe heart is the hollow, muscular organ in the chest whose four chambers pump blood through the lungs and then around the rest of the body.
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Written for biofideX in plain words, after checking these references:
- OpenStax Anatomy and Physiology 2e, 15.1 Divisions of the Autonomic Nervous System
- NCBI MeSH: Parasympathetic Nervous System
- NCI Dictionary of Cancer Terms: parasympathetic nervous system
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