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Action Potentials - Action Potentials If the total...

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Action Potentials If the total electrical activity of the cell results in a depolarization past threshold at the trigger zone , then the neuron will fire an action potential . The opening of the voltage-gated Na + channels on the axonal membrane causes the axonal membrane to depolarize beyond 0 mV and peak at ~ +35mV. The VG-Na + channels inactivate and delayed VG-K + channels open, allowing the efflux of K + from the cell, repolarizing the axonal membrane. These VG-K + channels remain open slightly longer than necessary to repolarize the axonal membrane, resulting in a slight overshoot of the RMP. In contrast to local potentials, APs are all-or-none , non-decremental , and irreversible . Refractory Periods The slight overshoot of the RMP at the end of the AP results in a period of resistance to further stimulation known as a refractory period. The absolute refractory period is the time when no stimulus, no matter how strong, can trigger an AP. This occurs as long as the VG-Na + gates are open or in the inactivated state. This is because if the open or inactivated VG-Na
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