From Khan Academy starting from 1:25, the narrator, while talking about the Electrochemical gradients, said that sodium ions would naturally want to diffuse down when having a high concentration up here and a low concentration down there.
My question is Why would sodium ions want to go down just because of one side is more positive than the other, I mean, isn't the same charges repelling each other? I don't think the degree of positivity will enable them to be attracted to each other.

Could anyone help me explain this?

  • 3
    $\begingroup$ Please make sure the external links are supplementary and not essential parts of your question. Links rot over time, and your question becomes incomprehensible. Also, very few people have inclination of clicking random URLs, and even smaller number of them would watch a video, which is an objective waste of time and bandwidth. $\endgroup$
    – andselisk
    Mar 10, 2021 at 5:14

1 Answer 1


This has more to do with the diffusion gradient. Sodium ions move from the region of their higher concentration to a region of their lower concentration.

In the example given by you, I believe, there are additional negatively charged molecules present in the inner side of the membrane, resulting in an influx of sodium ions to balance the same. However, like charges do repel, so this influx is not indefinite, but only up to a certain extent- until the electrical potential difference across the membrane exactly balances the concentration gradient. This point is known as the equilibrium potential.

(This question and answer might be more appropriate in the Biology SE, I think).


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