Final answer:
The action potential traveling along the T-tubules is detected by the dihydropyridine receptor (L-type calcium channel). The T-tubules carry the action potential into the cell, triggering the opening of calcium channels in the adjacent sarcoplasmic reticulum (SR) and leading to the release of Ca²+ into the sarcoplasm, which initiates muscle fiber contraction.
Step-by-step explanation:
The action potential traveling along the T-tubule is detected by the dihydropyridine (DHP) receptor (L-type calcium channel).
The T-tubules carry the action potential into the interior of the cell, which triggers the opening of calcium channels in the membrane of the adjacent sarcoplasmic reticulum (SR), causing Ca²+ to diffuse out of the SR and into the sarcoplasm. It is the arrival of Ca²+ in the sarcoplasm that initiates contraction of the muscle fiber by its contractile units, or sarcomeres.
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