Neuron X is at its resting membrane potential of -65 mV, with standard resting membrane permeabilities, and standard intracellular and extracellular concentrations of sodium, potassium, chloride and calcium.

In which direction will K+ move across the membrane when its selective channel opens?

(there are only 3 options in this question)

Question

Neuron X is at its resting membrane potential of -65 mV, with standard resting membrane permeabilities, and standard intracellular and extracellular concentrations of sodium, potassium, chloride and calcium.

In which direction will K+ move across the membrane when its selective channel opens?

(there are only 3 options in this question)

BlackTom AI · Accepted Answer

At a resting membrane potential of −65 mV, the K+ equilibrium (Nernst) potential is more negative (≈ −90 to −95 mV), so the net electrochemical driving force pushes K+ out of the cell.

1. Relevant knowledge points and concepts
- Ion movement across membranes is determined by the electrochemical gradient: the sum of the concentration (chemical) gradient and the electrical gradient.
- The Nernst equation gives the membrane potential at which a particular ion is at electrochemical equilibrium (no net flux). For K+, typical intracellular [K+] ≈ 140 mM and extracellular [K+] ≈ 4 mM.
- If the membrane potential is more positive than E_K, the net driving force on K+ is outward; if more negative, the net driving force is inward.

2. Step-by-step reasoning
- Determine E_K using the Nernst equation (37°C approximation).
- Compare E_K to the actual membrane potential (Vm = −65 mV).
- The sign and magnitude of Vm − E_K indicate the net driving direction for K+.

3. Calculations (intermediate steps shown)
- Use the simplified Nernst form at 37°C: E_K ≈ (61.5 mV) · log10([K+]out / [K+]in).
- Plug values: E_K ≈ 61.5 · log10(4 / 140) = 61.5 · log10(0.02857).
- log10(0.02857) ≈ −1.544 → E_K ≈ 61.5 · (−1.544) ≈ −95.0 mV.
- Driving force = Vm − E_K = (−65) − (−95) = +30 mV. Positive driving force for a cation means net outward movement.

4. Why the correct answer is correct
- Because Vm (−65 mV) is less negative than E_K (≈ −95 mV), the concentration gradient (higher K+ inside) dominates over the electrical attraction, resulting in net efflux of K+ until the membrane potential moves toward E_K.

5. Why the other options are incorrect
- "In": The electrical gradient alone would attract K+ inward, but the combined electrochemical gradient at Vm = −65 mV favors outward flow because Vm is more positive than E_K.
- "No movement": Net movement is nonzero because Vm ≠ E_K; only at Vm ≈ E_K would there be no net flux.

6. Conclusion
- The net movement of K+ when its selective channel opens is Out, which matches the provided answer.

类似问题

Which of the following statements concerning the neuronal membrane at rest is correct?

The resting potential of a neuron is negative because _____________.

Which ONE of the following factors DOES NOT contribute significantly to the resting membrane potential?

If Na+/K+ ATP-ase were inhibited in a resting neuron, which voltage would the neuron ultimately reach over a long period of time?

Increasing the expression of which membrane protein in a resting neuron would bring RMP closer to threshold voltage?

Which ONE of the following statements about the resting membrane potential of a neuron is NOT CORRECT?

The resting potential of a cell is negative because

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