Question: step 1

Answer: Calcium ions rush into muscle fibers

Question: step 2

Answer: Calcium binds to troponin

Question: step 3

Answer: Troponin changes shape and exposes actin binding site

Question: step 4

Answer: Myosin heads bind to actin binding site making a cross bridge

Question: step 5

Answer: Myosin heads do a powerstroke (using ADP and P) which slides actin and decreases length of sarcomere (Z line to Z line)

Question: step 6

Answer: ATP causes release of myosin head from actin binding site (cross the myosin head is free to repeat the cycle as long as calcium is in and the ATP available)