# Why is membrane potential not zero at equilibrium?

For the squid giant axon, the membrane potential computed by the Goldman equation is -60mV. And the Nernst potentials are (the differences between the K+ and the Na+'s Nernst potential and the membrane potential let the mechanism work):

  K+ = -74mV
Na+ = 55mV
Cl- = -60mV


I am wondering if the membrane potential is 0mV, whether the K+ and Na+ Nernst potentials still cause the mechanism to work, so can 0mV be a reasonable value? (That is, I think the value of potential is not important at all as long as the mechanism works well, is this true?)

• You have to consider that there are plenty of voltage-sensitive channels that will open at 0mV so, no, you will not be likely to have an equilibrium at 0mV with the "classic" amount and type of channels on the membrane.
– nico
Sep 22 '12 at 11:08
• Not only are you battling the electronic potential, you're also battling chemical potentials. I'll let a cellular physiologist handle the answer. Sep 23 '12 at 23:18
• Rephrased a little, why do neurons need to have nonzero resting potential, given that most of the driving force is in chemical gradients? See this answer: biology.stackexchange.com/questions/8811/…
– Luke
Jul 13 '13 at 17:17
• let all the protein rot and the membrane degrade and you'll get zero potential for sure. Aug 12 '13 at 18:14

## 1 Answer

The value of the membrane potential does not affect the location of the resting potential. The membrane potential affects only the fraction of channels that are open, thus allowing net current to change, which allows for the depolarization and repolarization of the membrane (the action potential). During the action potential, the resting potential does not change.

The value of the resting potential is governed only by the distribution of ions (how many are on one side of the membrane vs. how many are on the other). This is relatively constant even as ions cross the membrane for the action potential; it is really not a very large fraction of ions moving at all compared to the reservoir they are in, so the reversal potentials are preserved over time.