Do the proteins or the spaces change size during contraction explain your answer

An action potential in the motor neuron causes ACh to be released into the synaptic cleft. Binding of ACh to sarcolemma receptors initiates graded potentials. How does the shape change of these proteins lead to contraction? ... Myosin heads bind to the newly exposed myosin-binding sites on actin to form cross bridges.

Agroup of engineering students from purdue university reported that its licking machine, modeled after a human tongue, took an average of 364 licks to get to the center of a tootsie pop. twenty of the group's volunteers assumed the licking challenge-unassisted by machinery-and averaged 252 licks each to the center.