[refid]

For nerve signal Action potential, when Na+ ion move into the membrance and K+ move outside how can there be a charge difference since they are both postive ions?

[Yggdrasil]

The Na/K pump moves two potassium ions into the cell and three sodium ions outside the cell.  This creates a charge gradient.

[refid]

charge gradient is that because 3 na+ outside and 2K+ inside , unequal distrubution?

[Yggdrasil]

Yes.  In effect, the Na/K pump moves one unit of positive charge outside the cell/one unit of negative charge inside the cell.