Muscle fibers

[Lionzebra]

Why do all times you eg. do bicep curls once very light and one very heavy you still use the same number muscle fibers. It is according to the principle of "all or nothing".
I do not understand why same number of muscle fibers can lift both light and heavy.
I do not understand what musclefibers are.

 

[MonsterGear]

muscle fibers are fast, slow, fast activate with greater weight, slow are durable and operate at low loads, they are durable