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Lecture 19

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McGill University
PHGY 210
Ann Wechsler

Lecture 19 Remember that the upper proximal stomach is for storage, while the lower distal stomach is for mixing. No peristalsis in the proximal stomach, gastric peristalsis starts 1/3 of the way on the distal stomach, moving down towards the sphincter. The GI peristalsis is propagated contraction caused by local enteric reflexes in response to local distension. The amplitude of the stimulus leads to increased magnitude of the contraction. Frequency, direction, velocity of the contraction are controlled by the electrical characteristics of the smooth muscle. Electrode testing in the proximal stomach measures a straight line, a steady electrical signal. If electrodes are in the distal stomach smooth muscles records an unstable resting membrane potential, 10-15mV in size, lasting 1 to 4 seconds each, recurring at regular intervals. ALL cells at the same level share the same synchronized rhythm, but if they are delayed on the longitudinal muscle fibres, the rhythm is the same, but there is displacement, like sequential activation. The basic electrical rhythm is always present, regardless of the position, a property of the muscles itself in the stomach. Sometimes, secondary signals may appear at the peak of the depolarization, this second signal is called the ERA (electrical response activity). When an ERA occurs, the signal appears synchronously around circumference, but sequentially on the longitudinal side. The presence of ERA limits the number of contraction per unit time. The origin of the ECA is NOT neuronal, it is manifested in the muscle itself, it is a property of the muscle itself. The spikes are caused by Ach or stretching of the muscle, dependent upon calcium. Spread does not require neuronal support. The number of spikes is directly proportional to the magnitude of the stimulus. The maximal frequency of contractions of the stomach is limited by the frequency of the BER itself. The peristaltic contraction itself requires the integrity of the Enteric Nervous System. The amplitude is determined by the ma
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