The resting membrane potential of a cell:
Is dependent on the permeability of the cell membrane to K+ being greater to Na+ REF: Ganong, 22nd edition, BRS physiology, 4th edition page 11 Ionic Basis of nerve Resting Membrane Potential: Resting membrane potential is potential difference across the cell membrane in millivolts. Which is by convention -70 Mv Resting membrane potential is established by diffusion potential that results from concentration differences of permeable ions. And each permeable ion attempts to derive the membrane potential towards its equilibrium potential. Resting membrane potential (-70 mV) is close to equilibrium potential of K+ and C1-- (both -85 mV) and far away from the equilibrium potential of Na+ ( +65 mV). That means at rest the nerve membrane is more permeable to K+ than Na+ Na+ is actively transpoed out of neurons and other cells and K+ is actively transpoed into cells, but because of K+ permeability at rest is greater than Na+ permeability. Therefore, K+ channels maintain the resting membrane potential. Ionic Basis of nerve Action Potential: Depolarization causes rapid opening of the activation gates of Na+ channels and thus Na+ conductance promptly increases. Thus the membrane potential is driven towards the equilibrium potential of Na+ ion (+65 mV) Thus the rapid depolarization during upstroke is due to inward Na+ current Depolarization slowly opens K+ channels and increases K+ conductance to even higher levels than at rest. The combined effect of closing Na+ channels and greater opening of K+ channels make the K+ conductance higher than the Na+ conductance and membrane potential is repolarized. Thus repolarization is caused by outward K+ current. The K+ conductance remains higher than at rest for some time after closure of Na+ channel and the membrane potential is driven more closer to K+ equilibrium potential than at rest. This is called as undershoot.
Is dependent on the permeability of the cell membrane to K+ being greater to Na+
Falls to zero if Na+/K+ ATPase in membrane is inhibited
Is equal to the equilibrium potential for K+
Is equal to the equilibrium potential of Na+