Compare the action potentials of contractile cardiac muscle. autorhythmic cardiac muscle and skeletal muscle
In cardiac muscles, the action potential is initiated by the sinoatrial node that travels down the conduction system and spreads throughout the atrial and ventricular muscle fibers, called the contractile fibers. The resting potential of a healthy cardiomyocyte is approximately -90 mV. As the action potential is initiated by the SA node their is rapid depolarisation due to the opening of voltage-gated fast Na+ channels. Then comes a plateau stage in which there is maintained depolarization. This occurs due to the opening of voltage-gated slow Ca+2 channels and the closing of some K+ channels. The third and final phase is repolarisation. It occurs due to voltage-gated K+ channels and the closing of Ca+2 channels.
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