When you stimulate the nerve electrically, the muscle contracts; why? When you turn off the ...

You and your lab partner use a living nerve and muscle preparation to study muscle contraction. When you stimulate the nerve electrically, the muscle contracts; why? When you turn off the stimulator but add a high concentration of caffeine to the fluid surrounding the tissues, the muscle contracts; why (speculate on possible sites/mechanisms of action)? When curare (which blocks neuromuscular transmission) is added with caffeine, contraction occurs; why (speculate, and how does this alter your previous answer)? Can you identify a single site of action from this information? If not, what additional experiment would narrow your choices?