Impulse Conduction to Myocardium

Impulse Conduction to Myocardium - twists the ventricles...

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Impulse Conduction to Myocardium The SA node signal travels at 1 m/sec through both atria. Depolarization of the atria results in Ca +2 influx and contraction of the atrial muscle. The fibrous skeleton of the cardiac muscle insulates the depolarization of the atria from the ventricles. When the depolarization reaches the AV node, the signal travels slightly slower at about 0.05 m/sec. This delays the depolarization of the ventricular muscles and allows time for the ventricles to fill. The signal then travels very quickly through the AV bundle and Purkinje fibers, spreading throughout the ventricular muscle. The papillary muscles receive the signal first, contracting and stabilizing the AV valves through tension on the chordae tendineae. Ventricular systole begins at the apex and progresses up through the ventricular walls. The fibrous skeleton and the spiral arrangement of cardiomyocytes
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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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