What happens when a neuron at rest is stimulated to a level that reaches threshold?

The correct answer is: it fires an action potential.

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.

answer: b: experiments that showed that all cells are similar in how they metabolize and in their composition

explanation: