Explain the roles of actin and myosin in muscle contraction.?

so the actin sits on top of the myosin with an ADP bound to myosin. When calcium binds to troponen, it moves tropomyosin away on the actin so myosin heads can bind at 90 degrees. Think of a vine on a fence for tropomyosin. This is the crossbridge phase. Then power stroke phase occurs when the myosin heads make a 45 degree angle with the mysoin base. ADP leaves and ATP can bind to myosin which detaches the myosin head from actin. Then ATP is hydrolyzed and the myosin heads can move back to 90 degrees (recovery phase). THen the whole process starts over