Final answer:
Action potentials are electrical signals generated by neurons. The frequency of action potentials depends on the strength of the stimulus voltage. The size of individual action potentials does not change with an increase in stimulus voltage.
Step-by-step explanation:
The action potential is an electrical signal generated by nervous tissue. The resting membrane potential in neurons is around -70 mV, and during depolarization, the membrane voltage rises rapidly to around +30 mV. The frequency of action potentials is determined by the strength of the stimulus voltage.
In the given information, the amplitude is 30 mV and the duration is 500 msec. However, specific frequencies for stimulus voltages of 30 mV and 45 mV are not provided.
Regarding the size (amplitude) of individual action potentials, it does not change when the stimulus voltage is increased from 30 mV to 45 mV. Action potentials are all-or-none events, meaning they either happen or they don't, and their size remains the same regardless of the stimulus voltage.