Well, let's suppose the channel is a specific ion channel, and it only allows the movement of these cat ions. It doesn't allow the movement of the Anion. So as we open it up, what happens is because of this concentration difference that exists between the two sides, these positively charged ions will begin to move spontaneously from this side to this side. But what happens? Over time, the rate of movement begins to decrease until the rate of movement is equal to zero. The question is, why does that actually take place?