Answer:
Explanation:
This is because once a Voltage Gated Sodium Channels closes up after depolarization, they can not be reopened.The transmission of action potential is such a way that they are propagated one after the other in a forward direction, and never backwards. Thus once a sodium channel depolarizes,it closes up, to under go a shot rest.No matter the strength of the next stimulus it will not open. Then the channel ahead of it opens to depolarise to conduct action potential, this again after shut opening closes up for the channel ahead to open. This short period of rest when the sodium channels closes up is called refractive period. However after sometime of rest the rested sodium channels open, from the inactivated stage to conduct action potential.
