<prompt> Which among the following statement regarding skeletal and cardiac muscle is falseBoth require calcium for excitation contraction couplingThe excitation contraction coupling of skeletal muscle is independent of extracellular calciumBoth have graded contractionPlateau phase is seen in action potential of cardiac muscle. Repeat, 09  <response>: Ans: c Both have graded contraction Ref: Ganong 22nd edp.79Cardiac action potentialAction potential can be defined as the sequence of changes in the membrane potential in an excitable cell due to opening and closure of differention channels after application of a threshold stimulus.Phases of action potentialPhase 0 - Opening of voltage gated Na channel.Phase 1 - closure of sodium chan-nel- leads to initial rapid depolarization.Phase 2 - plateau phase- due to opening of L type Ca2channels.Phase 3 - final repolarization due to closure of Ca2 channels K efflux.Phase 4 - resting membrane potential. 