During muscle contraction, the sarcoplasmic reticulum (SR) releases calcium through which specific channels?
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Correct answer: Ryanodine receptors (RyR)
The RyR are calcium-release channels located in the SR membrane. They are opened when they receive a signal from the DHPR (voltage sensors) in the T-tubules, allowing calcium to flood the sarcoplasm and initiate contraction. DHPR senses the voltage change but does not itself release SR calcium.
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