Enteric nervous system
The enteric nervous system (ENS) or intrinsic nervous system is one of the main divisions of the autonomic nervous system and consists of a mesh-like system of neurons that governs the function of the gastrointestinal system.
The ENS is capable of autonomous functions such as the coordination of reflexes; although it receives considerable innervation from the autonomic nervous system, it can and does operate independently of the brain and the spinal cord. Its study is the focus of neurogastroenterology.
ENS function can be damaged by ischemia. Transplantation, which had been described as a theoretical possibility in earlier versions of this article, is now (as of 2011) a clinical reality in the United States and is performed at a number of approved centers.
The ENS consists of some one hundred million neurons, one thousandth of the number of neurons in the brain, and about one tenth the number of neurons in the spinal cord. [Number of neurons in human spinal cord = 1 billion (from Kalat, J.W., Biological Psychology, 6th Edition, 1998, page 24).] The enteric nervous system is embedded in the lining of the gastrointestinal system.
The neurons of the ENS are collected into two types of ganglia: myenteric (Auerbach's) and submucosal (Meissner's) plexuses. Myenteric plexuses are located between the inner and outer layers of the muscularis externa, while submucosal plexuses are located in the submucosa.
The enteric nervous system has been described as a "second brain" for several reasons. The enteric nervous system can operate autonomously. It normally communicates with the central nervous system (CNS) through the parasympathetic (e.g., via the vagus nerve) and sympathetic (e.g., via the prevertebral ganglia) nervous systems. However, vertebrate studies show that when the vagus nerve is severed, the enteric nervous system continues to function.
In vertebrates the enteric nervous system includes efferent neurons, afferent neurons, and interneurons, all of which make the enteric nervous system capable of carrying reflexes and acting as an integrating center in the absence of CNS input. The sensory neurons report on mechanical and chemical conditions. Through intestinal muscles, the motor neurons control peristalsis and churning of intestinal contents. Other neurons control the secretion of enzymes. The enteric nervous system also makes use of more than 30 neurotransmitters, most of which are identical to the ones found in CNS, such as acetylcholine, dopamine, and serotonin. More than 90% of the body's serotonin lies in the gut, as well as about 50% of the body's dopamine, which is currently being studied to further our understanding of its utility in the brain.
The enteric nervous system has the capacity to alter its response depending on such factors as bulk and nutrient composition. In addition, ENS contains support cells which are similar to astroglia of the brain and a diffusion barrier around the capillaries surrounding ganglia which is similar to the blood–brain barrier of cerebral blood vessels.
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See also 
- John Barton Furness (15 April 2008). The Enteric Nervous System. John Wiley & Sons. ISBN 978-1-4051-7344-5. Retrieved 16 January 2013.
- Barlow AJ, Wallace AS, Thapar N, Burns AJ (May 2008). "Critical numbers of neural crest cells are required in the pathways from the neural tube to the foregut to ensure complete enteric nervous system formation". Development 135 (9): 1681–91. doi:10.1242/dev.017418. PMID 18385256.
- Burns AJ, Thapar N (October 2006). "Advances in ontogeny of the enteric nervous system". Neurogastroenterol. Motil. 18 (10): 876–87. doi:10.1111/j.1365-2982.2006.00806.x. PMID 16961690.
- "enteric nervous system" at Dorland's Medical Dictionary
- Template:Gershon MD. The Second Brain Harper 1998 p17
- Linhares GK, Martins JL, Fontanezzi F, Patrício Fdos R, Montero EF (2007). "Do lesions of the enteric nervous system occur following intestinal ischemia/reperfusion?". Acta Cir Bras 22 (2): 120–4. doi:10.1590/S0102-86502007000200008. PMID 17375218.
- Gershon MD (April 2007). "Transplanting the enteric nervous system: a step closer to treatment for aganglionosis". Gut 56 (4): 459–61. doi:10.1136/gut.2006.107748. PMC 1856867. PMID 17369379.
- Boron, Walter F.; Boulpaep, Emile L. (2005). Medical Physiology. Elsevier Saunders. p. 883. ISBN 978-1-4160-2328-9.
- "The Enteric Nervous System". Retrieved 2008-11-29.
- Li,Ying;Owyang,Chung (September 2003). "Musings on the Wanderer: What's New in Our Understanding of Vago-Vagal Reflexes? V. Remodeling of vagus and enteric neural circuitry after vagal injury". American Journal of Physiology, Gastrointestinal and Liver Physiology 285 (3): G461–9. doi:10.1152/ajpgi.00119.2003.
- Pasricha, Pankaj Jay. "Stanford Hospital: Brain in the Gut - Your Health".
- Silverthorn, Dee U.(2007)."Human Physiology". Pearson Education, Inc., San Francisco, CA 94111.