Final answer:
True. T-tubules are invaginations of the sarcolemma of a muscle cell, allowing the action potential to reach the Sarcoplasmic Reticulum (SR) membrane.
Step-by-step explanation:
True.
T-tubules are indeed invaginations of the sarcolemma of a muscle cell. They are periodic invaginations in the sarcolemma, allowing the action potential to reach the membrane of the Sarcoplasmic Reticulum (SR). The arrangement of a T-tubule with the membranes of SR on either side is called a triad. The T-tubules carry the action potential into the interior of the cell, triggering the opening of calcium channels in the membrane of the adjacent SR, which is essential for muscle fiber contraction.