Which of the following statements about muscle contraction is true?

• A. Muscle contraction is initiated by the binding of myosin to troponin.
• B. ATP is required for the detachment of myosin heads from actin filaments.
• C. Calcium ions bind to tropomyosin to initiate muscle contraction.
• D. The sarcoplasmic reticulum releases sodium ions to trigger contraction.

Answer: (B)

Verified step by step guidance

1. Understand the role of calcium ions in muscle contraction: Calcium ions bind to troponin, not tropomyosin, to initiate muscle contraction. This binding causes a conformational change that moves tropomyosin away from the myosin-binding sites on actin filaments.
2. Recognize the role of ATP in muscle contraction: ATP is crucial for the detachment of myosin heads from actin filaments. After a power stroke, ATP binds to the myosin head, causing it to release from the actin filament, allowing the cycle to repeat.
3. Identify the function of the sarcoplasmic reticulum: The sarcoplasmic reticulum stores calcium ions and releases them into the cytosol to trigger muscle contraction, not sodium ions.
4. Clarify the role of myosin and troponin: Muscle contraction is not initiated by the binding of myosin to troponin. Instead, myosin binds to actin after troponin has moved tropomyosin away from the binding sites.
5. Evaluate the statements: Based on the understanding of muscle contraction mechanisms, the statement 'ATP is required for the detachment of myosin heads from actin filaments' is true.