• F Cerveró.
• Facultad de Medicina, Universidad de Bristol, Inglaterra.
• Rev Esp Enferm Dig. 1990 Aug 1; 78 (2): 79-88.

AbstractThe only non-general sensation that can be elicited from the gastrointestinal (GI) tract is that of pain, which can go from slight discomfort to severe pain. However, in certain parts of the intestine, such as the rectum and gastroesophagus, the sensation of pain can be preceded by a non-painful sensation of distension at low levels of stimulation. GI pain is often dull, poorly defined and difficult to pinpoint. In some cases, GI pain is projected to areas of the body distant from the source organ ("referred" pain). These characteristics indicate that the representation of internal organs within the nervous system is very imprecise. Experimental evidence based on behavioral, neurological and clinical testing shows that most GI pain is the result of activity in afferent visceral sensory fibers contained in sympathetic nerves, and that the afferent intestinal innervation by means of parasympathetic nerves is not essentially related to GI pain signalling and transmission. As for the peripheral sensory receptor coding mechanism in the intestine, experimental tests have shown the existence of specific visceral nociceptors in certain places (e.g., the biliary system) and the existence of a king of non-specific "intensity" receptors in others (e.g. the colon). In any case, the number of afferent nociceptive fibers in the intestine is minimal, and this accounts for the fact that large areas of the GI tract appear to be insensitive or to require considerable stimulation before pain can be elicited. The few afferent nociceptive fibers contained in the sympathetic nerves can excite quite a few second order neurons in the medulla spinalis, which in turn generate an extensive divergence within the medulla spinalis and brain stem, including at times long supraspinal branches. This divergent input can activate different motor, autonomous and sensory systems, thus triggering the general reactions which characterize visceral nociception: diffuse pain which is difficult to pinpoint, referred at times to somatic areas, and autonomous and somatic reflexes resulting in prolonged motor activity.

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