Question

The resting membrane potential in a nerve fibre:

• A. Is equal to the potential of ventricular muscle fibre
• B. Can be measured by surface electrodes
• C. Increases as extracellular K+ increases
• D. Depends upon K+ equilibrium

Hint:

At rest the membrane is mostly permeable to K+, so it sits near the K+ Nernst potential.

Answer 1

The Correct Option is D

Step 1: The resting membrane potential of a nerve fibre is about -70 mV. At rest the membrane is far more permeable to potassium than to other ions, so the potential lies close to the potassium equilibrium (Nernst) potential. Hence it depends mainly on the K+ equilibrium, option (d).

Step 2: Option (c) is incorrect as stated. When extracellular K+ rises, the K+ equilibrium potential becomes less negative, so the resting potential moves toward zero, that is it depolarises and becomes less negative, not larger in magnitude.

Step 3: Option (b) is wrong because the resting potential is a transmembrane potential measured with an intracellular microelectrode referenced to the outside. Surface electrodes record summed extracellular activity, not the true resting membrane potential of a single fibre.

Step 4: Option (a) is wrong because the resting potential of a nerve fibre (about -70 mV) differs from that of ventricular muscle (about -90 mV), and the two are not equal.