What event initiates cross-bridge formation during muscle contraction?

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Multiple Choice

What event initiates cross-bridge formation during muscle contraction?

Cross-bridge formation begins when calcium ions bind to the troponin complex on the thin filament. This Ca2+-troponin interaction causes tropomyosin to move away from the myosin-binding sites on actin, exposing them so a myosin head can attach and form a cross-bridge. The role of acetylcholine is to start the neural signal that leads to calcium release, not to directly trigger the cross-bridge; tropomyosin normally blocks the binding sites until calcium removes that block; and ATP hydrolysis energizes the myosin head but cross-bridge formation happens when the actin sites are exposed, not strictly after ATP has been hydrolyzed.

Cross-bridge formation begins when calcium ions bind to the troponin complex on the thin filament. This Ca2+-troponin interaction causes tropomyosin to move away from the myosin-binding sites on actin, exposing them so a myosin head can attach and form a cross-bridge. The role of acetylcholine is to start the neural signal that leads to calcium release, not to directly trigger the cross-bridge; tropomyosin normally blocks the binding sites until calcium removes that block; and ATP hydrolysis energizes the myosin head but cross-bridge formation happens when the actin sites are exposed, not strictly after ATP has been hydrolyzed.

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