<prompt> Plateau phase of cardiac muscle impulse conduction is due to inward motion of?KNaCaHCO3-  <response>: Ans. c Ca. Ref. Ganong, Physiology, 21s7pg,78Myocardial action potentialOccurs in atriol and ventricular myocytes and Purkinje fibers.CARDIAC ACTION POTENTIALMECHANISMPhase 0Rapid upstrokeVoltage-gated Na-channels open.Phase 1Initial repolariozationInactivation of voltage-gated Na balances K efflux.Phase 2PlateauCa2 influx through voltage-gated Ca2 channels balances K efflux. Ca2 influx triggers myocyte contraction.Phase 3Rapid repolarizationMassive K efflux due to opening of voltage-gated slow K channels closure ofvoltagegated Ca2 channels.Phase 4Resting potentialHigh K permeability through K channels. 