BIOL 4510 Lecture Notes - Osamu Shimomura, Roger Y. Tsien, Ryanodine Receptor 2

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22 Nov 2012
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The purpose of electrical depolarization (i. e. action potentials) is to initiate contraction. This process is called excitation-contraction coupling (e-c coupling). The electrical changes in the muscle cell (myocyte) induce an increase in intracellular ca2+ leading to the development of contraction. Muscle relaxation ensues following a decrease in intracellular ca2+. There are significant differences in e-c coupling in skeletal, cardiac and smooth muscle. Top figure showing action potentials (aps) in cardiac muscle vs skeletal muscle. In sk muscle aps are very short (3-5msecs) and a single ap generates a twitch force lasting 50-100 msecs. In cardiac muscle aps are much longer (~200msecs) and a single ap generates a twitch force lasting ~300 msecs. Bottom figure shows that aps in sk muscle have a rapid recovery time (short refractory time) and therefore sk muscle can be rapidly and repetitively stimulated which causes fusion of twitches and the generation of tetanus. In fact, sk muscle contraction usually involves tetanization of individual motor units.

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