The following is a list of events that occur during a muscle contraction. Place them in order: 4. The myosin head breaks down ATP and returns to the cocked position. 3. Binding sites on the actin become available and myosin creates a cross-bridge. 5. A molecule of ATP bind to the myosin head, breaking the crossbridge, detaching myosin from actin. 1. Calcium ions are released from the sarcoplasmic reticulum. 6. The myosin head pivots toward the center of the sarcomere, pulling the thin filament. 2. Calcium ions bind to troponin on the thin filaments.
The Correct Answer and Explanation is:
The correct sequence of events during a muscle contraction is as follows:
- Calcium ions are released from the sarcoplasmic reticulum.
This is the first step in muscle contraction. When a muscle receives a signal from a motor neuron, the action potential causes calcium ions (Ca2+) to be released from the sarcoplasmic reticulum (SR) into the cytoplasm. - Calcium ions bind to troponin on the thin filaments.
The calcium ions bind to troponin, a protein located on the actin filaments. This binding causes a conformational change in the troponin complex, which moves tropomyosin away from the myosin-binding sites on actin. - Binding sites on the actin become available and myosin creates a cross-bridge.
With the binding sites exposed, the myosin heads, which are part of the thick filaments, attach to the actin filaments. This forms the cross-bridge between actin and myosin, allowing the muscle contraction cycle to proceed. - The myosin head breaks down ATP and returns to the cocked position.
ATP is hydrolyzed by the myosin head, breaking it down into ADP and inorganic phosphate (Pi). This energy release causes the myosin head to “cock” back into its high-energy state, ready to initiate the power stroke. - A molecule of ATP binds to the myosin head, breaking the cross-bridge, detaching myosin from actin.
ATP binds to the myosin head, causing the myosin to detach from the actin filament, breaking the cross-bridge. The muscle relaxes temporarily in preparation for the next contraction cycle. - The myosin head pivots toward the center of the sarcomere, pulling the thin filament.
After ATP is hydrolyzed, the myosin head pivots, pulling the actin filaments toward the center of the sarcomere. This movement is called the “power stroke” and shortens the sarcomere, resulting in muscle contraction.
This entire sequence is known as the sliding filament theory, where the actin and myosin filaments slide past each other to shorten the muscle fibers, leading to muscle contraction.
