The strength of a stimulus (for example, whether you feel a slight pain versus an intense pain) determines the number of action potentials sent along an axon. as the graphs show, a strong stimulus produces more action potentials spaced more closely together than a weak stimulus.

the time between when a first action potential ends and a second action potential can be triggered is determined by the axon's refractory period. a second action potential cannot be triggered until the end of the refractory period.

which determines when refractory period ends?