Question:medium
The resting membrane potential in a nerve fibre:
The resting membrane potential in a nerve fibre:
Show Hint
At rest the membrane is mostly permeable to K+, so it sits near the K+ Nernst potential.
Updated On: Jun 24, 2026
- Is equal to the potential of ventricular muscle fibre
- Can be measured by surface electrodes
- Increases as extracellular K+ increases
- Depends upon K+ equilibrium
Show Solution
The Correct Option is D
Solution and Explanation
Step 1: Start from the Goldman concept: the resting potential of a neuron is set by the ions to which the membrane is most permeable at rest. For a nerve fibre that ion is potassium, because resting K+ channels (leak channels) dominate.
Step 2: Since K+ permeability dominates, the membrane potential settles near the potassium equilibrium potential given by the Nernst equation. This is exactly why the resting potential depends on K+ equilibrium, confirming option (d).
Step 3: Test the others. Raising external K+ shrinks the K+ gradient, so the cell depolarises (moves toward zero) rather than the potential increasing, so (c) fails. The true membrane potential needs an electrode inside the cell, so surface electrodes in (b) cannot measure it. And a nerve fibre at about $-70$ mV is not equal to ventricular muscle at about $-90$ mV, so (a) fails.
Step 4: Only the statement linking the resting potential to potassium equilibrium survives.
\[\boxed{\text{Depends upon } K^+ \text{ equilibrium}}\]
Step 2: Since K+ permeability dominates, the membrane potential settles near the potassium equilibrium potential given by the Nernst equation. This is exactly why the resting potential depends on K+ equilibrium, confirming option (d).
Step 3: Test the others. Raising external K+ shrinks the K+ gradient, so the cell depolarises (moves toward zero) rather than the potential increasing, so (c) fails. The true membrane potential needs an electrode inside the cell, so surface electrodes in (b) cannot measure it. And a nerve fibre at about $-70$ mV is not equal to ventricular muscle at about $-90$ mV, so (a) fails.
Step 4: Only the statement linking the resting potential to potassium equilibrium survives.
\[\boxed{\text{Depends upon } K^+ \text{ equilibrium}}\]
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