And each one of these protein channels contains a binding side for our acetylcholine. As soon as the acetylcholine binds to our protein on the membrane of the postsynaptic cell, that will cause these channels to open up. And now the sodium ions found on the outside will begin to flow into the cell. As soon as they begin to flow into the cell, that will increase the concentration of our sodium inside the cell, increasing the positive charge, and that will lead to depolarization of the membrane, and that will cause an action potential. Now, the action potential will in turn lead to the contraction of our muscle. So this is exactly what we mean by the transfer of an electrical signal.