Multiple Choice
In the sliding filament model of skeletal muscle contraction, what is the primary role of Ca released from the sarcoplasmic reticulum?
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9. Muscle Tissue
Steps of Muscle Contraction
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In the steps of skeletal muscle contraction, what is the primary role of released from the sarcoplasmic reticulum?
A
It pumps a out of the muscle fiber to initiate the action potential
B
It breaks down acetylcholine in the synaptic cleft to terminate the motor neuron signal
C
It binds to myosin ATPase to directly hydrolyze ATP and power the power stroke
D
It binds to troponin, causing tropomyosin to shift and expose myosin-binding sites on actin
Verified step by step guidance1
Understand that calcium ions (Ca^{2+}) are released from the sarcoplasmic reticulum into the cytoplasm of the muscle fiber during contraction.
Recognize that the primary role of Ca^{2+} is to bind to the regulatory protein troponin, which is part of the thin filament in muscle fibers.
When Ca^{2+} binds to troponin, it causes a conformational change that moves tropomyosin away from the myosin-binding sites on actin filaments.
This exposure of myosin-binding sites allows the myosin heads to attach to actin, forming cross-bridges necessary for muscle contraction.
Therefore, the release of Ca^{2+} from the sarcoplasmic reticulum initiates the interaction between actin and myosin, enabling the contraction cycle to proceed.
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