ENTEROCEPTION

Receptors present in the hollow viscera respond to extreme dilation, to contraction or spasm (colic), and to chemical irritation. These sensations are translated as pain and, when the affected organ is in the abdominal cavity, are often accompanied by reflex contraction of the abdominal muscles and cessation of abdominal breathing.

Referred pain, although important in human medicine, is of doubtful significance in animals. Pain impulses from the viscera share spinal cord pathways with sensory impulses arising from cutaneous zones that do not necessarily overlie these viscera but develop at the same embryological level. Because these pathways are much more often used by impulses from the cutaneous zones, it is not surprising that the brain misinterprets the origin of the much less frequent pain impulses from the viscera. The most widely known example is the pain referred to the presternal region, neck, shoulders, and inner aspect of the left arm in humans with angina pectoris, which is a lack of oxygen to the heart tissue due to an inadequate blood supply.

Small cutaneous zones have been identified in the cow as being related through the nervous system to certain abdominal organs. These zones become hyper­sensitive when the corresponding organs are diseased. It is interesting that these zones broadly coincide with the acupuncture points specified in the animal “maps” from China that have become known to the Western world in recent years.