Practice question · Put in order
Trace WHY the inside of the resting neuron ends up negative. Put the causal steps in order.
- At rest, open K+ channels vastly outnumber open Na+ channels.
- K+ diffuses out of the cell, down its concentration gradient.
- Potassium (K+) is far more concentrated inside the neuron than outside.
- The membrane potential settles near the K+ equilibrium value, close to -70 mV.
- Each K+ leaving carries positive charge out, making the inside more negative.
Hints
- Start with what is unequal (the gradient), then what the membrane lets through (permeability).
- The negativity is a CONSEQUENCE of positive K+ leaving, so charge loss comes before the final voltage.
Show the answer
- Potassium (K+) is far more concentrated inside the neuron than outside.
- At rest, open K+ channels vastly outnumber open Na+ channels.
- K+ diffuses out of the cell, down its concentration gradient.
- Each K+ leaving carries positive charge out, making the inside more negative.
- The membrane potential settles near the K+ equilibrium value, close to -70 mV.
Why
Because the membrane leaks K+ readily and K+ is high inside, K+ exits and drags positive charge out, leaving the interior negative until the potential rests near the K+ equilibrium. This is why it settles near E_K rather than midway between the ions.
Practise Resting Potential
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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?
- A neuron's potassium equilibrium potential is about −90 mV, yet the membrane actually rests at about −70 mV.…
- Select every statement that is TRUE of the resting potential.
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