Question

how did the action potential at R1 or R2 change as you increased the stimulus voltage above the threshold voltage

Answer 1

The action potential did not change.

The action potential did not change because once the threshold voltage is reached, the event is all or none, The action potential is always a full response. There is no such thing as a strong or weak action potential.

The all-or-none law is a principle that states that the strength of a response of a nerve cell or muscle fiber is not dependent upon the strength of the stimulus. If a stimulus is above a certain threshold, a nerve or muscle fiber will fire.so that means ther will be a response or no response, there is no such thing as partial response or fulll response.