Toproduce membranedepolarization,acurrent stimulus of sufficient intensity to exceedthe outward K current must be applied to the cell.If the depolarizing stimulus raises the membranepotentiala threshold value, sodiumabovechannels within the membrane change theirconformation and open their ion-selective pore
To produce membrane depolarization, a current stimulus of sufficient intensity to exceed the outward K current must be applied to the cell. If the depolarizing stimulus raises the membrane potential above a threshold value, sodium channels within the membrane change their conformation and open their ion-selective pore
allowing Na to enter the cell driven by theelectrochemical gradient. The open sodiumchannels raise the membrane potential towardtheequilibriumpotential of sodium (65 mV)andset into motion the intricate and preciselycoordinated series of ion channel openings andclosings leading to the characteristic actionpotential
allowing Na to enter the cell driven by the electrochemical gradient. The open sodium channels raise the membrane potential toward the equilibrium potential of sodium (65 mV) and set into motion the intricate and precisely coordinated series of ion channel openings and closings leading to the characteristic action potential
B.ActionIonsPotentialPhasesandAcrossMembrane:The action potential is divided into 5 phases, ie Phase0, 1, 2, 3, and 4.OmV03100msA-85mVNa+Nat NatOutsideMembranceintsideCa2+K+K+,CrPumpExchangerChannelcurrents
K+,ClChannel currents Pump Exchanger K+ Ca2+ Na Na+ + Ca2+ 100ms Outside 0mV Na+ intside Membrance -85mV 0 1 2 3 4 B. Action Potential Phases and Ions Across Membrane: The action potential is divided into 5 phases, ie Phase 0, 1, 2, 3, and 4
Phase O: fast upstrokeRapid depolarizationNa+ channels open (fast channel),Na+ rapidly entersthe cell through Na+ channel (fast channel) across the cellmembraneOmV国100ms-85mVNa+NatOutsideMembranceintsideCK+,CIChannel currentsPumpExchanger
Phase 0: fast upstroke Rapid depolarization Na+ channels open (“fast channel”), Na+ rapidly enters the cell through Na+ channel (fast channel) across the cell membrane
Phase l: The initial rapid phase of repolarization1)InactivationofNa+channels2) K+ channels rapidly open and close causing a transientoutwardcurrent.OmV100ms-85mVNatNaOutsideMembranceintside24aK,ClChannel currentsPumpExchanger
Phase 1: The initial rapid phase of repolarization 1) Inactivation of Na+ channels 2) K+ channels rapidly open and close causing a transient outward current