Neurons have inputs from many different cells that can be excitatory or inhibitory. Before action potentials are initiated, neurons sum these multiple inputs which either cause depolarization or hyperpolarization.
The typical threshold value to trigger an action potential is -50 millivolts.
Once the threshold value is reached, voltage-gated sodium channels open.
Local depolarization occurs at the spot in which the voltage-gated sodium channels open, which causes the potential of the cell to rise to positive values.
The opening of voltage-gated sodium channels causes sodium influx into the cell and depolarization.
Voltage-gated potassium channels open at positive potential values triggering an efflux of potassium.
The efflux of potassium results in repolarization of the cell, where the cell electric potential decreases to negative values again.
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