A model of the voltage-gated sodium channel is put forward suggesting that the four S4 voltage-sensors behave as screw-helices making a series of discrete transitions that carry one elementary charge for each notch of the screw helix. After the channel has been activated by the first two steps R reversible arrow P reversible arrow A in all four domains, followed by a voltage-independent rearrangement, it is opened by a third cooperative step A reversible arrow B in domains I, II and III in conjunction with hydration. Inactivation is a voltage-dependent process controlled by the third step A reversible arrow I in sensor IVS4, and the closing of the channel is brought about its dehydration. From the inactivated steady state the channel may be reopened by a fourth step, I reversible arrow C in sensor IVS4 and rehydration. The computed kinetics of the model are shown to conform closely with those observed experimentally.