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Unformatted text preview: * Contractile cells * Autorhythmic (or automatic) cells. * Autorhythmic cells exhibit PACEMAKER POTENTIALS. * Depolarization is due to the inward diffusion of calcium (not sodium as in nerve cell membranes). * Depolarization begins when: * the slow calcium channels open (4), * then concludes (quickly) when the fast calcium channels open (0). * Repolarization is due to the outward diffusion of potassium (3). Myocyte Autorhythmic cells Sheet of cells In Contractile cells: Cardiovascular System * depolarization is very rapid & is due to the inward diffusion of sodium (0). * repolarization begins with a slow outward diffusion of potassium, but that is largely offset by the slow inward diffusion of calcium (1 & 2). So, repolarization begins with a plateau phase. Then, potassium diffuses out much more rapidly as the calcium channels close (3), and the membrane potential quickly reaches the 'resting' potential (4)....
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- Fall '10