I'd have to agree with Zzulu. The CNS controls how much of the muscle contracts and how forceful the contraction is. Inexperienced lifters cannot control the motor fuctions of the muscle nearly as well as experienced lifters, who have the ability to utilize more of the muscle they have. Although Jay is right, muscle is responsible, I believe that the CNS plays a much larger role. It is the regulator of muscle function.
This is why i think that mental outlook and attitude during a lift can have such a profound effect on a lift or even a workout. If you are pumped and determined, your mind will try harder to recruit more muscle fibers. This is why I believe if you are psyched and mentally optomistic about a lift, you will have a much better chance of making the lift. Take Deceiver for example. His mind is set that 200 pounds is a barrier. The kid is strong as hell, and if he believes he can lift the weight, I'm totally sure he could.
I think that CNS and the manipulation of it to maximize strength gains is one of the biggest differences between bodybuilders and powerlifters. Why isn't Coan weaker than Coleman? Ronnie has a lot more muscle mass than Ed Coan does, but Ed Coan is stronger. This must be due to the fact that Ed Coan can better recruit muscle fibers and contract them more forcefully. In all fairness though, Ronnie Coleman doesn't train for strength; if he did, and learned to use the CNS as equally as Coan has, i believe that Ronnie would be stronger.
This topic also brings to mind amazing feats performed during people during times of great mental stress. Have any of you ever heard of those people that lift cars to save people? During the times of great emotional distress the mind doesn't have the option to synthesize some protein and build some muscle, it relies on the CNS to make up for that and deliver strength.
Btw, i'm not saying that Ronnie Coleman isn't strong, I am just saying that factoring in relative size, Ed Coan is simply much stronger.