The action potential is generated by depolarization of voltage-gated channels beginning at the axon hillock, and spreading successively from one set of gates to the next. The is accomplished as depolarization at one set of gates pulls ions from the next set and depolarizes it, spreading from one set of gates to the next. The axon potential is self-propagated, and all or none. As the action potential passes each set of gates, first the Na+ gates open producing depolarization, then the K+ gates open producing repolarization. The depolarization actually reverses the potential because so many N+ ions enter the cell. Likewise so many K+ ions leave the cell that hyperpolarization is briefly produced. Meanwhile, the depolarization has spread to the next set of ion gates.