Pretty self explanatory question. I have a basic grasp on the "How" and "Why" of Reversal/Action Potential in and between neurons, but this question lingers.

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    $\begingroup$ I’m not sure the question is quite clear: the repulsive force of the ions is necessary for their role (otherwise you wouldn’t get an electrochemical gradient across the membrane). $\endgroup$ Aug 21, 2012 at 8:58
  • $\begingroup$ The electrochemical gradients are estabished from movement and difference of each ion internal and external concentrations - K+intracell/K+extracell -, NOT between differing ions ie not between Na+ and K+. $\endgroup$
    – user972
    Aug 21, 2012 at 15:10
  • $\begingroup$ Actually a fair point. $\endgroup$ Aug 21, 2012 at 15:20
  • $\begingroup$ I agree with rwst's response below, and just wanted to add that it's not the individual ion species that matter, but the fact that there are several ions, each with ion channels of varying permeabilities. Both sides of the membrane are electrically neutral, but the chemical potentials differ due to the channels. More specifically, the resting membrane potential exists because of the higher permeability of the K+ channels. $\endgroup$
    – jello
    Aug 21, 2012 at 20:42

1 Answer 1


The carriers of the charge are ions and they get repelled from each other well enough. Other than their charge there is only the size in which they differ (for all practical purposes). This means, as long as we are talking about membrane potential, the actors are just a mix of 1+ ions which don't come near each other. When size matters, for example in an ion channel, we are talking about single particles, so there is no action of a repulsive force between K+ and Na+.

From another angle: The charge is a force that emerges from a sea of particles, regardless if they are all of one kind or mixed K+/Na+. If you talk about a force between K+ and Na+ then you would have to separate all 10^15 or so K+ ions from 10^15 or so Na+ ions which is simply impossible, as they are mixed up.




  • $\begingroup$ Ok, in other words.. the ions are too small and not uniformly purposed/moving to have such any such disruptive effect from hindering the AP process. Thanks for the insight, if I could trouble you for a source you surely would receive the BEST answer and this would be a resolved question. $\endgroup$
    – user972
    Aug 21, 2012 at 15:20
  • $\begingroup$ This is elementary physics/chemistry. I don't need to show that atoms/molecules have no purpose, they undergo Brownian motion except when spatially hindered by a channel molecule. OK, I'll give suitable Wikipedia links. $\endgroup$
    – R Stephan
    Aug 21, 2012 at 16:14
  • $\begingroup$ Please forgive my elementary knowledge :) A good habit to source answers nonetheless, thanks! $\endgroup$
    – user972
    Aug 21, 2012 at 16:54
  • $\begingroup$ Also remember that it is not Na+/K+ ions which go through the ion channels, but the solvated ions which are encased in a highly ordered water solvation sphere around them. The different sized sovlation spheres is what causes the difference in sizes for the ion channels. In a cell, negative ions would screen the positive charges from each other unless they were very close. $\endgroup$
    – Nick
    Aug 24, 2012 at 13:20

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