The gut as a neurological organ

We refer to the gut as a neurological organ to emphasize the particular importance of the nervous system in the regulation of digestive functions, given that the gastrointestinal tract is innervated by five different classes of neurons: intrinsic enteric neurons, vagal afferents, spinal afferents, parasympathetic efferents and sympathetic efferents. Virtually each aspect of digestive activity is under the regulatory influence of neurons, among which the enteric nervous system (ENS) plays the most important part. The ENS acts like a brain in the gut that functions independently of the central nervous system, contains programmes for a variety of gastrointestinal behaviours and governs the activity of all gastrointestinal effector systems according to need. Intrinsic sensory neurons supply the ENS with the kind of information that this system requires for its autonomic control of digestion, whereas extrinsic afferents notify the brain about any data that are relevant to energy and fluid homeostasis and the sensation of discomfort and pain. Many diseases of the gut, particularly the functional bowel disorders, seem to be related to dysfunction of the ENS and other components of the gastrointestinal innervation. The ENS and extrinsic afferents are hence prime targets for the therapeutic management of gut diseases and for the relief of the pain and discomfort associated with these disorders.