The enteric nervous system represents collections of nerve plexuses, formed by neurons, axons and dendrites which surround the gastrointestinal tract, pancreas and biliary tract. It can be considered as 'the brain in the gut'. It comprises the myenteric plexus of Auerbach (between the longitudinal and circular smooth muscle layers of the external muscle coat) and the submucosal plexus of Meissner (between the submucosa and the muscularis propria). Fibres project to glands, visceral muscle cells and blood vessels. The system controls gastrointestinal motility, blood flow, water and electrolyte transport, acid secretion, and various local reflexes in the gastrointestinal tract by the generation of stereotyped patterns of electrical activity.
There are three types of component neurons: sensory, associative or inter-neurons and motor neurons. Motor neurons may be excitatory (parasympathetic postganglionic) or inhibitory (NANC system). The myenteric plexus primarily regulates motility and the submucosal plexus regulates absorption and secretion. Extrinsic nerves supplying the small intestine regulate or modulate the activity of the enteric nervous system.
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