Nervous Control of Intestinal Motility

Abstract

The most important functions of the intestinal musculature are to transport the contents through the long tubular digestive tract and to ensure their adequate mixing and exposure to absorptive surfaces. The behaviour of the muscle associated with these functions is complex and highly adaptable to ensure the efficient utilisation of nutrients, even though feeding habits and diet may vary. The movements of the muscle depend on three primary factors: the intrinsic properties of the musculature itself, which undergoes rhythmic changes in excitability that vary along the intestine; the influence of circulating hormones; and the influence of nerves. The systems of nerves associated with the intestine are remarkable. Within the wall of the intestine is a complex network of intrinsic neurones, the enteric nervous system, which has connections with the muscle, mucosal cells and blood vessels of the gut wall, as well as with sympathetic ganglia and the central nervous system. Langley, in his book on the autonomic nervous system (1921), had already realised the relative autonomy of the enteric nervous system, and classified it as one of the three divisions of the autonomic nervous system, the others being the sympathetic and parasympathetic divisions. It is at first surprising that the total number of enteric neurones is similar to the total number of neurones in the spinal cord, but the enteric nervous system, like the spinal cord, controls an extensive system of muscle with a varied repertoire of movements. The enteric nervous system is also involved in the modulation of secretion, intestinal blood flow and probably absorption. Like the spinal cord, the enteric ganglia are reflex centres, receiving sensory information, integrating this information and influences from other centers and providing an output to effectors.