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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© 2015 Published by Elsevier Inc.