What control the frequency of signals for Action potentials?

Referring to following image, I would like to know on what control the frequency of signals for Action Potentials.
Does anyone have any suggestions?

Thanks in advance for any suggestions :>

Post Merge: 8 years ago

Referring to following videos, Voltage is the measure of potential energy generated by separated charges.
I would like to know on after signal is triggered through Hilllock, would it must go to the end of synaptic terminal? would signal disappear during AP process? and How do body handle this missing signal? would they re-generate signal if signal is detected no response from Synaptic Terminal?

Does anyone have any suggestions?
Thanks in advance for any suggestions

Best Action Potential explanation


The Nervous System, Part 3 - Synapses!: Crash Course A&P #10