An action potential is sure to fire, once_________ channels are open.
Volatge gated Na+
An action potential is an all or none phenomenon, that is once the threshold potential of -55mV is reached it is sure to fire, if not there will be no action potential generated. The threshold potential is -55mV because at -55mV the voltage gated Na+ channels open, which sets off a positive feedback loop leading to opening of more voltage gated Na+ channels in the next segment of the neuron, forming the action potential.