And these proteins allow ions to flow in or as a cell, the active transport or passive transport. Now, so today we're only going to look at this guy here, potassium ion. But notice that our resting electrical potential, the cell or our cell voltage, is generated by simply adding up the cell voltages of all these four ions. When we add all these guys up, we get our final cell voltage or the resting electrical potential. Now, today, to save time, I'm only going to show you for this potassium ion. You can do these on your own.