Now, we know that on the outside of the cell we have a higher concentration of sodium ions than on the inside of the cell. And what that means is if we did not have this cell membrane, these sodium ions would move down their electrochemical gradient from a high electric potential to a low electric potential. And this is essentially analogous to a marker moving from a high gravitational potential to a low gravitational potential in the following manner. So essentially, from physics, we know that because there's a positive charge on the outside and a negative charge on the inside, there will be an electric field that exists across the cell membrane. And so this electric field that points this way from the outside to the inside will create, will exert an electric force that will try to pull on these sodium ions. Let's focus on this sodium ion here.