Voltage-gated Na+ channels begin to open as the membrane potential increases to a defined voltage. At this point, the channel opens. The fractional conductance, a measure of how much current comes from a group of channels, is either 0% or 100% for a single channel - it is either open or closed. After the channel has been open for around 1ms, a plug blocks the channel, preventing ion transport and thus closing it. This causes hyperpolarisation. As the plug takes a couple of seconds to detach from the inner vestibule, it causes a refractory period, during which a new action potential cannot be formed. This is beneficial, as it prevents the backwards transmission of impulses, ensuring they always travel in the same direction.
Voltage-gated K+ channels are similar to voltage-gated Na+ channels, with their opening induced by an increase in membrane potential. However, the opening of voltage-gated K+ channels is delayed, taking longer to open compared to Na+ channels. This allows the channels to stay open for longer at higher membrane potentials. The plug allows the channel to be inactivated, just like Na+ channels. The current provided by the K+ channel depends on the voltage, due to Ohm’s law.