Answer:
The correct answer is: it fires an action potential.
Step-by-step explanation:
Neurons at rest have a resting potential that describes the differences in voltage across the membrane. When a depolarization current is applied onto the resting neuron, it can cause an action potential if the threshold is reached. This action potential describes a sudden electrical activity that is responding to the stimulus -the current- that arrived at said neuron. When the action potential occurs, the voltage-gated sodium channels in the membrane are opened and thus allow a big influx of this ion into the cell, increasing the membrane potential even more quickly.