In the sliding filament theory, what forms a cross-bridge within the sarcomere?

• A. The attachment of calcium ions to myosin
• B. The connection between actin filaments and the Z line
• C. The interaction between troponin and tropomyosin
• D. The binding of myosin heads to actin filaments

Answer: (D)

Verified step by step guidance

1. Understand the structure of the sarcomere, which is the functional unit of muscle contraction, consisting of actin and myosin filaments.
2. Learn about the sliding filament theory, which explains how muscles contract by the sliding of actin over myosin filaments.
3. Recognize that cross-bridges are formed when myosin heads bind to specific sites on actin filaments, initiating the contraction process.
4. Explore the role of calcium ions, which bind to troponin, causing a conformational change that moves tropomyosin away from the binding sites on actin.
5. Identify that the binding of myosin heads to actin filaments is the key event in forming cross-bridges, leading to muscle contraction.