Unformatted text preview: In the heart, tetanus is prevented by the long duration of the cardiac action potential. The refractory period and the contraction end almost simultaneously. No summation can occur as the myocardial cell has almost completely relaxed by the time another action potential takes place. C.2.9 Autonomic control of Autorhythmic cells : Sympathetic ("fight and flight") and parasympathetic ("rest and digest") divisions of the autonomic nervous system exert antagonistic responses on the heart rate. Parasympathetic system : Effects on the autorhythmic cells (SA node): Fig. 14-17b. • ACh activates muscarinic cholinergic receptors and acts by: • 1. Increasing the K + conductance (increased K + efflux) resulting in hyperpolarization of the pacemaker cells, • 2. Decreasing the Ca 2+ current (decreased Ca2+ influx) which slows the depolarization rate of the pacemaker potential. • Both actions combined result in a shorter duration of the action potential which leads to a decreased cardiac output...
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This note was uploaded on 12/26/2011 for the course KIN 205 taught by Professor Blaber during the Fall '09 term at Simon Fraser.
- Fall '09