In cardiac muscles, depolarization is due to influx of which ion ?

Ans. is 'a' i.e., Na+Action potential in cardiac muscles Normal RMP in myocardial fibers is about -90 mV The AP in myocardial fibers has 5 phases : 0, 1, 2, 3, 4.Phase 0 :- It is the phase of rapid depolarization and is due to opening of fast sodium channels.Phase 1 :- It is the initial phase of rapid repolarization. It is due to closure of fast Na+ channels.Phase 2 :- This is platen phase. It is due to opening of 'voltage gated slow Ca+ channels, also called calcium-sodium channels which causes calcium influx.Phase 3 :- This phase of final repolarization is due to opening of IC- channels. The membrane potential comes back to resting membrane potential.Phase 4 :- It is the resting phase, i.e., the phase of resting membrane potential.