The resting membrane potential of a typical large motor neuron is about -70 mV, which is much closer to the equilibrium potential of potassium (-90 mV) than that of sodium (+60 mV). The main reason is:

• A The sodium-potassium pump transports 3 Na+ out for every 2 K+ in
• B Intracellular impermeant anions exert an electrostatic pull on K+
• C Intracellular K+ concentration is higher than extracellular K+ concentration
• D At rest, the membrane is far more permeable to K+ than to Na+ ✓

Explanation

The resting potential is a weighted average of the equilibrium potentials of permeant ions, weighted by their conductances. Because resting K+ conductance greatly exceeds resting Na+ conductance (through leak channels), the potential sits near EK. Option C is true but merely explains why EK is negative; it is the high relative permeability that pulls Vm toward EK. The pump contributes only a few millivolts directly and maintains the gradients indirectly.

Reference: Ganong's Review of Medical Physiology, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.