Question

put the steps of muscle contraction in order from first (1) to last (5).
the sarcomere shortens.
calcium ions are released by a nerve cell.
the sarcomere is relaxed.
actin and myosin overlap completely.
actin and myosin are activated.

Explanation:

1. Initially, the sarcomere is in a relaxed state (step 1: "The sarcomere is relaxed").
2. Then, a nerve cell triggers the release of calcium ions (step 2: "Calcium ions are released by a nerve cell").
3. The calcium ions activate actin and myosin (step 3: "Actin and myosin are activated").
4. Activation leads to the sarcomere shortening as actin and myosin interact (step 4: "The sarcomere shortens").
5. Finally, actin and myosin overlap completely as the contraction progresses (step 5: "Actin and myosin overlap completely").

Answer:

1. The sarcomere is relaxed
2. Calcium ions are released by a nerve cell
3. Actin and myosin are activated
4. The sarcomere shortens
5. Actin and myosin overlap completely