refractory period notes draft

During the absolute refractory period, there are no action potentials occurring in the cell. This is due to the voltage gates sodium channels being inactivated. This occurs in the time frame directly after the depolarization. Following the absolute refractory period is the relative refractory period. During this refractory period, the voltage gated sodium channels are closed, however, the voltage gated potassium channels are open. This means that an action potential will most likely not occur unless there is a huge stimulus that causes a rush of positive potassium into the cell. These refractory periods are different when muscle twitches or tetanus occurs. Following a contraction, calcium is typically pumped away from the cell when the repolarization occurs. However, in a muscle twitch, action potentials happen quickly after one another and stops the calcium from being pumped away from the cell. This means that the left over calcium adds to the following contraction, leading to more force. In muscle tetanus, these contractions continue because the fast flow of action potentials causes the calcium to be pumped into the cell as fast as it is pumped out of the cell.