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General and gastric motility

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Physiology 3120
Tom Stavraky

Human Physiology Monday, March 29, 2010 “Gastro V” Motility • Basic principles of enteric smooth muscle (ESM); designed to move food along the GI tract and can accommodate a large meal  Can deal with a great degree of stretch; has an intrinsic (biophysical property, not influenced by nerves or hormones) response to stretch; skeletal muscle that is stretched for a period of time will increase tension for a period of time, and the tension will remain high as long as the muscle is stretched; in enteric smooth muscle, get an increase in tension initially, but relaxes over time if the stretch stimulus remains; think of it as a piece of Silly Putty; this property allows you to eat a large meal without feeling satiety until you’ve had enough; this phenomenon is called stress relaxation  Electrical properties; in skeletal muscle, voltage is negative inside the cell, and it doesn’t fluctuate; in ESM, in most parts of the GI tract, membrane potential oscillates (sinusoidal) over time; this membrane potential is called the slow wave; to initiate contraction, must induce an action potential across the cell membrane; APs typically occur at the peak of the slow wave (closer to threshold); contraction measured in mmHg (increases pressure); pressure increases during an AP; slow wave does not cause contraction, but does seem to dictate the number of
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