1. Muscle contraction

4. Myosin (thick filament)

5. Actin (thin filament)

6. Resting Sarcomere Myosin head has stored energy Troponin Tropomyosin
ADP P
Troponin
Tropomyosin
ADP
Active sites of actin are covered P

7. Step 1 In Muscle Contraction
Ca++ Bind to Troponin, exposing active site of actin
ADP P
Ca++
Tropomyosin
Ca++
ADP P
Troponin
Active sites of actin are covered

8. Step 2 In Muscle Contraction
Myosin cross bridge binds to the active site on the actin filament
ADP P
Ca++
ADP
Ca++ P

9. Step 3 In Muscle Contraction
The myosin head pivots toward the center of the sarcomere
The ADP and the Phosphate group are released
ADP P
Ca++
Ca++
ADP P

10. Step 4 In Muscle Contraction
Another ATP molecule attaches and the myosin head detaches from the active site of the actin
ATP
Ca++
Ca++
ATP

11. Step 5 In Muscle Contraction
The detached myosin head is reactivated as it splits the ATP into ADP and a phosphate group
ADP P
Ca++
Ca++
ADP P

12. The cycle repeats until the calcium ions are pumped out of the myofibril