Plateau of cardiac action potential is due to
Correct Answer: Opening of voltage-activated slow calcium channels
Description: Ans. c (Opening of voltage-activated slow calcium channels) (Ref. Ganong Physiology 22nd/pg. Chapter 29).In contrast to skeletal muscle:1. Cardiac muscle action potential has a plateau, which is due to Ca2+ influx2. Cardiac nodal cells spontaneously depolarize, resulting in automaticity3. Cardiac myocytes are electrically coupled to each other by gap junctions# Slow influx of calcium is responsible for the plateau phase of the action potential.Myocardial action potentialPhase 0Rapid depolarizationRapid sodium influx; these channels automatically deactivate after a few msPhase 1Early repolarizationEfflux of potassiumPhase 2PlateauSlow influx of calciumPhase 3Final repolarizationEfflux of potassiumPhase 4Restoration of ionic concentrationsResting potential is restored by Na+/K+ ATPase; there is slow entry of Na+ into the cell decreasing the potential difference until the threshold potential is reached, triggering a new action potential.
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