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Multiple Choice
Which ion stimulates shape changes at the beginning of skeletal muscle contraction?
A
Chloride (Cl-)
B
Sodium (Na+)
C
Potassium (K+)
D
Calcium (Ca2+)
Verified step by step guidance
1
Understand that skeletal muscle contraction begins with a signal from the nervous system, specifically a motor neuron releasing acetylcholine at the neuromuscular junction.
Recognize that acetylcholine binds to receptors on the muscle cell membrane, leading to depolarization and the generation of an action potential that travels along the sarcolemma and into the T-tubules.
Learn that the action potential triggers the release of calcium ions (Ca2+) from the sarcoplasmic reticulum into the cytoplasm of the muscle cell.
Understand that calcium ions (Ca2+) bind to troponin, a regulatory protein on the actin filament, causing a conformational change that moves tropomyosin away from the binding sites on actin.
Realize that this shape change allows myosin heads to bind to actin, initiating the cross-bridge cycle and muscle contraction.