What is the correct order of events in the sliding filament theory of muscle contraction? 1. Myosin head binds to actin 2. Calcium ions bind to troponin 3. Myosin cross-bridges bend, pulling actin toward center of sarcomere 4. ATP is split into ADP and P 5. Tropomyosin moves to expose active sites of actin 6. Sarcoplasmic reticulum releases calcium ions 7. ADP and P released from myosin

The correct order is: 6) Sarcoplasmic reticulum releases calcium ions, 2) Calcium ions bind to troponin, 5) Tropomyosin moves to expose active sites of actin, 4) ATP is split into ADP and P, 1) Myosin head binds to actin, 7) ADP and P released from myosin, 3) Myosin cross-bridges bend, pulling actin toward center of sarcomere.

Explanation:

The ability to contract is an important property of the muscle cells and is fundamental to animals because muscles not only make locomotion possible but are also responsible for the correct functioning of organs (including the heart).

The mechanism behind muscle contraction is the sliding of filaments in a structure called sarcomere, which mostly involves the presence of actin and myosin filaments.

For muscle contraction to happen, there needs to be a stimulus coming from the nerve that innervates said muscle. This stimulus generates the release of calcium ions that will bind to a protein called troponin and will lead to the exposure of the active site of actin so it can bind to the myosin head. This process requires ATP.