Muscle action potential, establishing a gradient?

Ok for an action potential to occur there has to be depolarization of the axon, this is caused by rapid entry of Na+ into the membrane (Sodium influx). The membrane potential went from being negative in the inside to positive in the inside. Keep in mind K+ is always flowing out gradually. Once this occurs you then have the falling phase or polarization. Since you have a positive charge in the inside, there is a driving force for K+ to the outside (potium efflux). The membrane potential is restored. Negative charge in the inside, positive charge on the outside.