Muscles are relaxed

myosin is not bound to actin

myosin is bound to actin

cross bridges have formed

myosin has bent toward the center of the sarcomere

myosin is not bound to actin

Explanation:

When the muscle relaxes the verve stimulation stops and the calcium is then pumped back into the sarcoplasmic reticulum which causes a break in the link between actin and myosin. Actin and myosin, therefore, return to their unbound state causing the muscle to relax.

the oldest known insects are believed to live around 400 millions ago as suggested by the fossil records.   some plants having woody stems also evolved during this time.

after the evolution of insects the first four legged species or the tetrapods evolved in shallow freshwater habitats from the intermediate species approximately 397 million years ago. the tetrapods went on conquering the land giving rise to amphibians, reptiles, mammals and birds.

the major split in tetrapods first occurred 340 million years ago branching off from amphibians.

363 million years ago when the carboniferous period began the insects started roaming on land and taking flights, following which the four limbed tetrapods adapted in the terrestrial habitat.