Q. You are given the isolated skeletal muscle with its motor neuron intact. This preparation is arranged so that you are able to make electrophysiological measurements from the nerve and the muscle as well as mechanical measurements of muscle contraction. You view that if caffeine is added to the fluid bathing the preparation, the peak tension developed in a muscle twitch produced by stimulating the motor nerve is increased.

i. List all probable points at which caffeine may be exerting its effect.

ii. Caffeine is known to alter the transmembrane movement of calcium. What is (are) the possible site(s) at which caffeine is acting?

iii. High concentrations of caffeine cause an isolated muscle to contract in absence of any activity in the motor nerve. This contraction is not blocked by nicotinic antagonists like curare. Where and how is caffeine exerting its effects?