Plateau phase of cardiac muscle impulse conduction is due to inward motion of?
Ans. c (Ca++). (Ref. Ganong, Physiology, 21s7pg,78)Myocardial 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 ofvoltage=gated Ca2+ channels.Phase 4Resting potentialHigh K+ permeability through K+ channels.
K+
Na+
Ca++
HCO3-
Heart, Circulation, and Blood