Sensation in the gastrointestinal tract.

There are similarities between sensation in the gastrointestinal tract (GI tract) and somatic sensation. This review concentrates on parasympathetic (vagal) components of GI sensation rather than the sympathetic (splanchnic) elements. A wide range of enteroceptors have been described over the whole length of the gut which subserve several different sensory modalities. Fibres from these enteroceptors project to the medulla, primarily to the nucleus of the solitary tract. In the medulla there is considerable integration of afferent information from different parts of the GI tract. Regulatory peptides are present both in the brain and in the GI tract. It is likely that these peptides may play a role in the modulation of sensory information in the medulla. Parallels may be drawn at a receptor level between somatic sensation and sensation in the GI tract. More centrally, sensory mechanisms relating to the gut seem less highly organized than in somatic sensation. This reduced influence of the central nervous system in GI tract sensation may be explained by the presence in the gut of a highly sophisticated intrinsic nervous system, the enteric nervous system, which pre-programmes many of the functions of the GI tract.