Neuron X has standard resting permeabilities, and standard intracellular and extracellular concentrations of sodium, potassium, chloride and calcium. When depolarised to +58mV by a strong, excitatory synaptic input, what direction will K+ move across the membrane if its selective channel were opened?
神经元 X 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。当受到强烈的兴奋性突触输入而去极化至 +58mV 时，如果其选择性通道打开，K+ 将向哪个方向跨膜移动？

Question

BlackTom AI · Accepted Answer

E_K (the K+ Nernst potential) is strongly negative (around −90 to −95 mV) under standard intracellular/extracellular concentrations, so at a membrane potential of +58 mV K+ will flow out.

1) Relevant concepts
- Nernst potential (E_ion) gives the membrane potential at which there is no net movement of that ion. 
- Driving force for an ion = V_m − E_ion. For a positively charged ion, a positive driving force corresponds to net outward movement (efflux).
- Typical physiological concentrations: [K+]_in ≈ 140 mM, [K+]_out ≈ 4 mM.

2) Step-by-step reasoning and calculations
- Compute E_K using the Nernst equation (at ~37°C, simplified factor ≈ 61.5 mV):
  E_K = 61.5 mV × log10([K+]_out / [K+]_in)
  = 61.5 × log10(4 / 140)
  = 61.5 × log10(0.02857)
  log10(0.02857) ≈ −1.5441
  E_K ≈ 61.5 × (−1.5441) ≈ −95 mV (approximately).
- Driving force = V_m − E_K = (+58 mV) − (−95 mV) = +153 mV.
- A positive driving force for a cation means net outward movement. Thus, if K+-selective channels open, K+ will leave the cell.

3) Why this is correct
- Chemically, K+ is higher inside than outside so diffusion tends to drive K+ out. Electrically, the inside being strongly positive (+58 mV) repels positive K+ ions outward. Both components of the electrochemical gradient therefore favor efflux, so opening K+ channels produces K+ movement out of the cell until V_m approaches E_K.

4) Why other choices are wrong
- “No change”: incorrect because the membrane is far from E_K; opening channels will cause current flow. 
- “In”: incorrect because for K+ to move inward the membrane potential would need to be more negative than E_K (to attract K+ in); +58 mV is much more positive than E_K, so K+ is driven out.

Conclusion: K+ will move Out, which matches the provided correct answer.

类似问题

Exposure to Cholera Toxin, can result in diarrhoea resulting in severe dehydration due to excessive water loss. Why might this be detrimental to neuronal homeostasis and what is the consequence?

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?

In a neuron with a resting membrane potential of -65mV, the distribution of which ion across the neuronal membrane represents the greatest electrical potential?

In a two-compartment model of a cell with a K +- and Cl --permeable membrane and a 10-fold excess of K + in the inside compartment, how would the membrane potential change if all K + ions were replaced by Cl - ions?

Which statement regarding membrane potential and equilibrium potential is true?

A group of neurons expresses a pump which actively transports Vz2- into the cell, and also expresses a limited number of Vz2- leak channels in the cell membrane. Which voltage would most closely represent EVz in these neurons?

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单