Autonomic nervous system
Say it: aw-tuh-NOM-ik NUR-vus SIS-tum
The autonomic nervous system is the division of the nervous system that runs involuntary functions such as heart rate, digestion and gland secretion.
Also: ANS, involuntary nervous system, visceral nervous system
Definition
What is the autonomic nervous system?
The autonomic nervous system, or ANS, runs the internal organs without conscious effort. It controls cardiac muscle, the smooth muscle of organs and blood vessels, and glands, keeping heart rate, blood pressure, breathing, digestion and body temperature within useful ranges. It is steered mainly by the hypothalamus and the brainstem.
Its two main divisions usually work against each other. The sympathetic division, whose nerves leave the spinal cord in the chest and lower back regions, readies the body for fight or flight: it speeds the heart, widens the airways and pupils, sends blood to skeletal muscle and slows digestion. The parasympathetic division, whose nerves leave the brainstem and the sacral spinal cord, supports rest and digest: it slows the heart, narrows the pupils and promotes digestion. The enteric nervous system of the gut is often counted as a third division.
Autonomic pathways use a chain of two neurons. In both divisions, the first neuron releases acetylcholine onto nicotinic receptors in a ganglion. Parasympathetic second neurons release acetylcholine onto muscarinic receptors, while most sympathetic ones release norepinephrine onto adrenergic receptors. The adrenal medulla acts as a modified sympathetic ganglion that releases epinephrine into the blood.
Word parts
Where does the term “autonomic nervous system” come from?
- auto-
- selfGreek autos
- -nomic
- law, ruleGreek nomos
Practice it
Where you'll meet it
Quizzes that use it
Related
Terms that go with it
- Central nervous systemThe central nervous system is the brain and spinal cord, the part of the nervous system that takes in sensory input, integrates it and sends out commands.
- HomeostasisHomeostasis is the body's ability to keep internal conditions, such as temperature, blood glucose and pH, steady while conditions around it change.
- AcetylcholineAcetylcholine is the neurotransmitter motor neurons use to make skeletal muscles contract, and a key messenger in the autonomic nervous system and brain.
- 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.
- Blood pressureBlood pressure is the force that circulating blood exerts on the walls of the arteries, recorded as systolic over diastolic pressure in mm Hg.
- ReceptorA receptor is a protein, on a cell's surface or inside it, that binds a specific signaling molecule and triggers a response in the cell.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Anatomy and Physiology 2e, 15.1 Divisions of the Autonomic Nervous System
- OpenStax Biology 2e, 35.4 The Peripheral Nervous System
- NCI Dictionary of Cancer Terms: autonomic nervous system
- NCBI MeSH: Autonomic Nervous System
Last updated
Spotted a mistake? Tell us and we'll correct it.
Practice Neuroscience
Free neuroscience quizzes, with an explanation for every answer.
See the Quizzes