What initiates cross-bridge formation in the sliding filament model's first step?

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Study for the Anatomy and Physiology Muscular System Test. Prepare with flashcards and multiple choice questions; each question provides hints and explanations. Get ready to excel in your exam!

Multiple Choice

What initiates cross-bridge formation in the sliding filament model's first step?

Explanation:
Calcium ions released from the sarcoplasmic reticulum bind to troponin C on the thin filament, causing the troponin-tropomyosin complex to move and uncover the myosin-binding sites on actin. With these sites exposed, energized myosin heads can attach to actin and form cross-bridges, kicking off the cross-bridge cycle. ATP binding to the myosin head occurs later in the cycle to detach and re-cock the head, not to initiate cross-bridge formation. Sodium influx relates to triggering the action potential, which ultimately leads to calcium release, but is not the direct trigger for cross-bridge formation.

Calcium ions released from the sarcoplasmic reticulum bind to troponin C on the thin filament, causing the troponin-tropomyosin complex to move and uncover the myosin-binding sites on actin. With these sites exposed, energized myosin heads can attach to actin and form cross-bridges, kicking off the cross-bridge cycle. ATP binding to the myosin head occurs later in the cycle to detach and re-cock the head, not to initiate cross-bridge formation. Sodium influx relates to triggering the action potential, which ultimately leads to calcium release, but is not the direct trigger for cross-bridge formation.

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