The resting potential of a cell is negative because

Question

BlackTom AI · Accepted Answer

At rest there is an excess of K+ inside the cell and the membrane is permeable chiefly to K+, so the membrane potential is driven toward the K+ equilibrium potential (negative inside).

1) Relevant concepts
- Electrochemical gradients: ions diffuse down concentration gradients; electrical gradients oppose further net movement.
- Nernst equilibrium potential for a single ion: Eion = (RT/zF) ln([ion outside]/[ion inside]); for K+ this is usually negative because [K+]in >> [K+]out.
- Membrane permeability and the Goldman equation: the resting membrane potential is a weighted average of equilibrium potentials, weighted by relative permeabilities (PK, PNa, PCl).
- Na+/K+ ATPase maintains concentration gradients but is not the primary determinant of the instantaneous resting potential.

2) Step-by-step reasoning
- Typical concentrations: [K+]in ≈ 140 mM, [K+]out ≈ 4 mM. Using the Nernst equation at 37°C gives the K+ equilibrium potential, which strongly influences Vm because PK >> PNa.
- K+ diffuses out via leak channels, leaving behind unbalanced negative charges (proteins, organic anions). This creates an electrical gradient that eventually balances the outward K+ diffusion; that balance is the negative equilibrium potential.

3) Calculation (intermediate steps shown)
- E_K ≈ 61.5 mV × log10([K+]out/[K+]in)
- E_K ≈ 61.5 × log10(4/140) = 61.5 × log10(0.02857)
- log10(0.02857) ≈ −1.544 → E_K ≈ 61.5 × (−1.544) ≈ −95 mV
- Resting Vm is typically ≈ −60 to −75 mV because some Na+ permeability (ENa ≈ +61 mV) shifts the value slightly away from EK toward zero, as described by the Goldman equation.

4) Why the correct answer is correct
Because K+ leak channels provide the dominant pathway for charge movement at rest, the membrane potential is pulled toward EK (a negative value). The large intracellular K+ excess and high K+ permeability are therefore the main cause of the negative resting potential.

5) Why other common choices are incorrect
- “The Na+/K+ pump alone causes the negativity”: the pump maintains gradients but contributes only a small direct electrogenic effect (~−3 to −5 mV); permeability to K+ is the dominant factor.
- “Negatively charged proteins inside are the sole cause”: proteins contribute fixed negative charge but do not determine Vm without selective membrane permeability to ions.
- “Cl– distribution alone sets Vm”: Cl– can influence Vm in some cells, but because membrane permeability to K+ is much higher, K+ predominates.

6) Conclusion
The negative resting potential is chiefly because of the excess of intracellular K+ combined with high membrane permeability to K+, confirming the provided answer.

The resting potential of a cell is negative because单项选择题

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?

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