What is the function of the transverse tubules in a skeletal-muscle fiber? A) They store the calcium ions that are the main source of activation for the cross-bridge cycle. B) They form the Z lines that mark the end of each sarcomere. C) They allow action potentials to propagate deep into the center of skeletal muscle cells. D) They manufacture and store ATP. E) They run in parallel with the myofibrils, and have abundant Ca²⁺-ATPase proteins for pumping Ca²⁺ back into the sarcoplasmic reticulum.

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The transverse tubules (T-tubules) are invaginations of the muscle cell membrane that allow action potentials to rapidly propagate deep into the center of skeletal muscle fibers. This allows for a coordinated contraction of the entire muscle fiber.

What Is the Function of the Transverse Tubules in a Skeletal-Muscle