Practice question · Multiple choice
A neuron's potassium equilibrium potential is about −90 mV, yet the membrane actually rests at about −70 mV. Why does the resting potential fall short of the potassium equilibrium value instead of sitting on it?
Hints
- The resting membrane is very permeable to K+, but K+ is not the only ion with a channel open.
- Ask what a small, steady inward trickle of positive charge would do to a voltage otherwise set by potassium.
Show the answer
D. Because the membrane is not perfectly selective; Na+ leaks inward.
Why
The resting potential is a compromise, and the −20 mV gap is where you see it happening: potassium dominates but a small Na+ leak drags the membrane up from E_K. The pump is not the source, it contributes a few millivolts of its own, and blocking it lets the potential decay over minutes rather than milliseconds.
Practise Resting Potential
The app has 5 more questions on this lesson, and keeps your place in the course. Psychology I is free to start.
More questions on Resting Potential
- Sort each ion by where it is more concentrated across the membrane of a resting neuron.
- A neuron at rest sits at about −70 mV. Why is the membrane NOT electrically neutral at rest?
- Trace WHY the inside of the resting neuron ends up negative. Put the causal steps in order.
- Select every statement that is TRUE of the resting potential.
- The sodium-potassium pump runs constantly in every neuron, and the brain spends a large share of its entire…