So let's begin by focusing on membrane channels. So let's suppose we're going to focus on a specific type of ion. Let's say the sodium ion. 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.