The Gut Contains Afferent Neurons That Relay Information to the Central Nervous System

The gut contains afferent neurons that course to CNS centers through nerves associated with the autonomic nervous system. Vagal afferent nerves of the Gl tract are associated with both mechanoreceptors and chemoreceptors and thus provide input to the CNS about changes in gut muscle tension and chemical conditions in the gut lumen.

There are also afferent neurons from the gut that connect with the CNS through the splanchnic nerves, which also con­tain sympathetic efferent fibers. 'Γhese afferent neurons convey signals arising from mechanoreceptors and chemoreceptors in the gut. In contrast to the vagal afferent nerves, however, the splanchnic afferents usually signal the presence of patho­logical conditions, such as overdistention of the gut wall, inflammation, or the presence of noxious chemicals or sub­stances in the gut lumen. These nerves are distributed into the serosal surfaces and mesentery of the gut, in addition to the muscular and mucosal layers. These splanchnic afferent nerves convey to the CNS the conscious perception of pain caused by abnormal pressure within the gut lumen, inflam­mation, the presence of noxious stimuli in the gut lumen, or the stretching of mesenteric attachments. Such nerve signals result in the intense pain response characteristic of such conditions as equine colic and gastric distention and volvulus in dogs. Painful stimuli from the gut usually evoke a sympathetic motor response, inhibiting gut motility and many glandular secretions.