Neuromechanical factors in GIT motility

      Motility of the large intestine involves formation and propulsion of faeces. Combined methods were used to construct temporal maps of movements and intraluminal pressure to determine the motor patterns generated by different mechanical conditions in isolated colon. The role of excitatory and inhibitory enteric pathways was inferred from mechanical states of the intestinal muscle, and demonstrated that activation of enteric ascending excitatory and descending inhibitory reflex pathways propel the contents. In empty segments of colon spontaneous slowly propagating neural motor complexes (MMCs) are modified by the physical consistency of the contents to shape and propel the faeces. Increasing the surface area of boluses, lowering the viscosity of contents increase in a p5redictable way the speed of propulsion. Solid faeces in the form of pellets are formed by a process that involves MMCs arriving from the proximal colon interacting with a slow myogenic pacemaker activity at the colonic flexure. Using high resolution, EMCCD camera and loading a calcium indicator into multiple myenteric ganglia, the temporal activation of myenteric neurons along the colon can be visualized, demonstrating for the first time that coordinated neuronal firing pattern is responsible for the MMCs. Despite the complexity of colonic movements, two fundamental neural mechanisms, namely a spontaneous, content independent slowly migrating motor activity coupled with a content dependent neuromechanical loop, shape and adapt propulsion to the physical characteristics of contents. A simplified model of the neuromechanical loop shows that few realistic factors appear sufficient to generate the rich repertoire of intestinal motility.
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