How do animal muscles move in order to perform an action or movement?

How do animal muscles move in order to perform an action or movement?    

(Ans) When a nerve impulse reaches the muscle. At cellular level muscle cell changes its shape and shorten.

The muscle cells have special proteins, which in response to nervous electrical impulses change their shape and their arrangement in the muscle cell. The new arrangement of proteins makes the muscle cells shorter resulting in the contraction of muscles.