Unformatted text preview: twists the ventricles slightly, efficiently contracting the ventricles. Contraction of Cardiomyocytes Most cardiomyocytes (except the nodal cells) have a stable resting membrane potential of ~-90 mV. The depolarization phase of cardiomyocytes is very brief and due to the stimuli-dependent opening of Na + channels and the rapid influx of Na + . The action potential peaks at ~+30 mV and the Na + channels quickly close. Unique to cardiomyocyte action potentials is the plateau phase, which lasts for 200 to 250 msec . Stimulated by the depolarization of the membrane, Ca +2 channels on the plasma membrane and the SR open, increasing the intracellular concentration of Ca +2 resulting in sustained muscular contraction. During repolarization the Ca +2 channels close and K + channels open resulting in an efflux of K + , returning the cell to rest. (See Figure 7) Figure 7...
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- Fall '10
- Anatomy, cardiomyocytes, fibrous skeleton, SA node signal, stable resting membrane