Resting membrane potential is mainly due to -

Ans. is 'b' i.e., K+ Genesis of RMPo The cell membrane is selectively permeable. Due to presence of potassium leak channels K+ ions are freely permeable but permeability of Na+ is much less . In the generation of RMP, following sequence of events occur :-i) K+ diffuses out of cell along its concentration gradient (K+ concentration is very high inside the cells and very low in ECF).ii) The diffusion of K+ produces an intracellular negativity (due to non-diffusible protein anion in the cells) which is not nullified by the diffusion of Na+ in the opposite direction (membrane is impermeable to Na+) or diffusion of Cl- in same direction (Cl- concentration is already very high in ECF in comparison to ICF).iii) So, intracellular negativity is produced which opposes outward diffusion of K+ and when the equilibrium is reached, the inward force on K+ due to electrical gradient balances outward force on K+ due to concentation gradient.iv) Finally, at equilibrium inner side of cell is negatively charged with respect to outer side, and resting membrane potential is produced.o So, the RMP is principally due to concentration difference (chemical difference) of K+ in ECF and ICF. In neurons, the resting membrane potential is usually about -70 mV, which is close to the equilibrium potential for K+. Here, it is worth noting that RMP is close to the equilibrium potential of K+ but the value of RMP is exactly same as equilibrium potential of Cl-. It is because other ions also diffuse through membrane, though their effect is very little.