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Autonomic nervous system

Autonomic nervous system
Autonomic nervous system innervation
Details
Identifiers
Latinautonomici systematis nervosi
MeSHD001341
TA98A14.3.00.001
TA26600
FMA9905
Anatomical terminology

The autonomic nervous system (ANS), formerly referred to as the vegetative nervous system, is a division of the nervous system that operates internal organs, smooth muscle and glands.[1] The autonomic nervous system is a control system that acts largely unconsciously and regulates bodily functions, such as the heart rate, its force of contraction, digestion, respiratory rate, pupillary response, urination, and sexual arousal.[2] This system is the primary mechanism in control of the fight-or-flight response.

The autonomic nervous system is regulated by integrated reflexes through the brainstem to the spinal cord and organs. Autonomic functions include control of respiration, cardiac regulation (the cardiac control center), vasomotor activity (the vasomotor center), and certain reflex actions such as coughing, sneezing, swallowing and vomiting. Those are then subdivided into other areas and are also linked to autonomic subsystems and the peripheral nervous system. The hypothalamus, just above the brain stem, acts as an integrator for autonomic functions, receiving autonomic regulatory input from the limbic system.[3]

Although conflicting reports about its subdivisions exist in the literature, the autonomic nervous system has historically been considered a purely motor system, and has been divided into three branches: the sympathetic nervous system, the parasympathetic nervous system, and the enteric nervous system.[4][5][6][7] Some textbooks do not include the enteric nervous system as part of this system.[8] The sympathetic nervous system is often considered the "fight or flight" system, while the parasympathetic nervous system is often considered the "rest and digest" or "feed and breed" system. In many cases, both of these systems have "opposite" actions where one system activates a physiological response and the other inhibits it. An older simplification of the sympathetic and parasympathetic nervous systems as "excitatory" and "inhibitory" was overturned due to the many exceptions found. A more modern characterization is that the sympathetic nervous system is a "quick response mobilizing system" and the parasympathetic is a "more slowly activated dampening system", but even this has exceptions, such as in sexual arousal and orgasm, wherein both play a role.[3]

There are inhibitory and excitatory synapses between neurons. A third subsystem of neurons has been named as non-noradrenergic, non-cholinergic transmitters (because they use nitric oxide as a neurotransmitter) and are integral in autonomic function, in particular in the gut and the lungs.[9]

Although the ANS is also known as the visceral nervous system and although most of its fibers carry non-somatic information to the CNS, many authors still consider it only connected with the motor side.[10] Most autonomous functions are involuntary but they can often work in conjunction with the somatic nervous system which provides voluntary control.

  1. ^ "autonomic nervous system" at Dorland's Medical Dictionary
  2. ^ Schmidt, A; Thews, G (1989). "Autonomic Nervous System". In Janig, W (ed.). Human Physiology (2 ed.). New York, NY: Springer-Verlag. pp. 333–370.
  3. ^ a b Allostatic load notebook: Parasympathetic Function Archived 2012-08-19 at the Wayback Machine - 1999, MacArthur research network, UCSF
  4. ^ Langley, J.N. (1921). The Autonomic Nervous System Part 1. Cambridge: W. Heffer.
  5. ^ Jänig, Wilfrid (2008). Integrative action of the autonomic nervous system : neurobiology of homeostasis (Digitally printed version. ed.). Cambridge: Cambridge University Press. p. 13. ISBN 978052106754-6.
  6. ^ Furness, John (9 October 2007). "Enteric nervous system". Scholarpedia. 2 (10): 4064. Bibcode:2007SchpJ...2.4064F. doi:10.4249/scholarpedia.4064.
  7. ^ Willis, William D. (2004). "The Autonomic Nervous System and its central control". In Berne, Robert M. (ed.). Physiology (5. ed.). St. Louis, Mo.: Mosby. ISBN 0323022251.
  8. ^ Pocock, Gillian (2006). Human Physiology (3rd ed.). Oxford University Press. pp. 63–64. ISBN 978-0-19-856878-0.
  9. ^ Belvisi, Maria G.; David Stretton, C.; Yacoub, Magdi; Barnes, Peter J. (1992). "Nitric oxide is the endogenous neurotransmitter of bronchodilator nerves in humans". European Journal of Pharmacology. 210 (2): 221–2. doi:10.1016/0014-2999(92)90676-U. PMID 1350993.
  10. ^ Costanzo, Linda S. (2007). Physiology. Hagerstwon, MD: Lippincott Williams & Wilkins. p. 37. ISBN 978-0-7817-7311-9.

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