What has to happen before a second nerve impulse can be generated?
The sodium channels that initiate depolarization have to go from an inactive state to a closed state. The sodium channel has two gates-an inactivation gate and a regular gate. Both of them are capable of completely blocking the channel alone, but they can both be shut at the same time too. Most of the time, the regular gate is the only one that’s closed. During a nerve impulse, the regular gate opens, sodium rushes in, and the cell is depolarized (this conducts the nerve signal down the cell). When the depolarization hits its peak, the inactivation gate snaps shut, followed quickly by the regular gate. It takes a little while for the inactivation gate to open back up. While it’s closed, that channel can NOT open no matter what- and the cell is incapable of generating a second nerve impulse. This is called the absolute refractory period. As soon as the inactivation gate opens up again (the regular gate stays closed), that cell is again sensitive to signal and can generate a nerve impuls
