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.
神经元 X 的静息膜电位为 -65 mV，具有标准的静息膜通透性，以及标准的细胞内和细胞外钠、钾、氯和钙浓度。

In which direction will Na+ move across the membrane when its selective channel opens?
当 Na0选择性通道打开时，Na0将沿哪个方向穿过膜？

(there are only 3 options in this question)
（本题只有 3 个选项）

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.
神经元 X 的静息膜电位为 -65 mV，具有标准的静息膜通透性，以及标准的细胞内和细胞外钠、钾、氯和钙浓度。

In which direction will Na+ move across the membrane when its selective channel opens?
当 Na0选择性通道打开时，Na0将沿哪个方向穿过膜？

(there are only 3 options in this question)
（本题只有 3 个选项）

BlackTom AI · Accepted Answer

E_Na is approximately +60 to +66 mV under standard intra- and extracellular concentrations, so Na+ will flow into the neuron.

1) Relevant concepts
- Nernst (equilibrium) potential for an ion (E_ion) determines the electrical potential at which there is no net flow of that ion.
- The electrochemical driving force = Vm − E_ion. For a positively charged ion (Na+), a negative driving force (Vm < E_Na) produces net inward movement; a positive driving force (Vm > E_Na) would drive it outward.
- Typical physiological conditions: [Na+]out ≫ [Na+]in and the resting membrane potential is negative (here Vm = −65 mV).

2) Step-by-step reasoning
- Use the Nernst equation to estimate E_Na for standard concentrations.
- Compare Vm (−65 mV) to E_Na. If Vm is much more negative than E_Na, Na+ is driven inward by both chemical and electrical gradients.

3) Calculations (intermediate steps)
- Typical values: [Na+]out ≈ 145 mM, [Na+]in ≈ 12 mM.
- Nernst (37 °C): E_Na ≈ 61.5 mV × log10([Na+]out/[Na+]in).
- Compute ratio: 145/12 ≈ 12.083. log10(12.083) ≈ 1.082.
- E_Na ≈ 61.5 × 1.082 ≈ +66.6 mV.
- Driving force = Vm − E_Na = (−65) − (+66.6) = −131.6 mV. The large negative driving force means strong inward movement of the positively charged Na+.

4) Why the correct answer is correct
- Both components of the electrochemical gradient (higher extracellular [Na+] and negative intracellular potential) favor Na+ entry when Na+ channels open. The membrane potential is far from E_Na, so opening a Na+-selective channel causes Na+ to flow into the cell until Vm moves toward E_Na.

5) Why the other choices are incorrect
- “Out” would require Vm to be more positive than E_Na (Vm > E_Na), which is not the case.
- “No net movement” would require Vm ≈ E_Na (~ +66 mV), but Vm is −65 mV, so substantial net inward flow occurs.

6) Conclusion
- Therefore Na+ will move into the neuron when its selective channel opens — answer: In (在).

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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