1. Christina Nappi,, Valentina Clinton Rachel Phillips Ainslie Lee, Dominique Simpson Period 4,

2. Muscle contraction  Muscle contractions function due to the Sliding Filament Theory, which allows myosin heads to attach to binding sites and create sliding motions.

3. Diagram of Filaments See page 192 Figure 6.7 (a)- (b)

4. Step 1  After an impulse creates an action potential across the sarcolemma, calcium ions are released from storage areas.  Shown of page 193 figure 6.8 (a)

5. Step 2  This release of calcium triggers the cell to contract.  As calcium binds to protein receptors on actin filaments. This exposes myosin binding sites on the actin after their shape/position has been changed on the filaments.  The myosin heads can attach to those binding sites so the heads start to search for a place to bind.  As shown on page 193, figure 6.8 (b)

6. Step 3  The myosin heads are “cocked”, and the myosin attaching to actin causes the heads to pivot to the center of the sarcomere.  The actin and myosin are still connected at this point, so the thin filaments are also pulled to the center of the sarcomere.

7. Step 3  The energy needed to release the myosin heads so they can continue to attach to binding sites on the filament later on comes from ATP.  After action potential ends and calcium ions are reabsorbed, the receptor proteins go back to their original shape. They block myosin from attaching, so the cell relaxes and contraction ends.  As shown on page 193, figure 6.8 (c)

8. The End