*Sarcomere is resting.

Tropomyosin is blocking binding site.

Myosin heads are holding on ADP + organic phosphate from previously used ATP.

1. Action potential in a motor neuron.

2. Release of acetylcholine at the myoneural junction.

3. The action potential spreads across the sarcolemma into the transverse tubules. (associated with sarcoplasm)

4. Sarcoplasm reticulum releases Ca+.

5. Ca+ binds troponin.

6. The Troponin/Tropomyosin complex moves to the side and exposes the binding site on actin.

7. Myosin head binds actin forming a "cross-bridge".

7.5. - myosin head releases ADP + inorganic Phosphate (The energy for the power-stroke came from the release of ADP + P_i)

8. Power-stroke occurs pulling actin in toward the H-zone.

9. The head must bind a new molecule of ATP to break the crossbridge.

10. Head splits the ATP and is ready to begin another cycle.

Review: EXAM III