Multiple Choice
In the cross-bridge cycle of muscle contraction, at which stage does ATP hydrolysis occur?
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9. Muscle Tissue
Steps of Muscle Contraction
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What triggers the release of calcium ions from the sarcoplasmic reticulum during muscle contraction?
A
The binding of acetylcholine to receptors on the muscle cell membrane
B
The depolarization of the muscle cell membrane
C
The hydrolysis of ATP by myosin heads
D
The binding of calcium ions to troponin
Verified step by step guidance1
Understand the role of the sarcoplasmic reticulum (SR) in muscle contraction: The SR stores calcium ions (Ca²⁺) and releases them when a muscle cell is stimulated, which is crucial for muscle contraction.
Identify the initial trigger for muscle contraction: The process begins with a nerve impulse that reaches the neuromuscular junction, causing the release of the neurotransmitter acetylcholine.
Explain the role of acetylcholine: Acetylcholine binds to receptors on the muscle cell membrane, leading to the opening of ion channels and an influx of sodium ions (Na⁺), which depolarizes the muscle cell membrane.
Connect depolarization to calcium release: The depolarization of the muscle cell membrane triggers the opening of voltage-gated calcium channels in the sarcoplasmic reticulum, leading to the release of Ca²⁺ into the cytosol.
Clarify the role of calcium ions: The released calcium ions bind to troponin, causing a conformational change that allows myosin heads to bind to actin filaments, ultimately leading to muscle contraction.
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