MusFIG 2: Schematic showing T-tubule structure in vertebrate muscle.

A. Illustraion of T-tubules spanning a muscle cell.
B. Diagram shows close apposition of the T-tubules with cisternae formed by the sarcoplasmic reticulum. The lumena of the T-tubules are continuous with the extracellular fluid and the membrane depolarization during an action potential diffuses across the T-tubule membrane.

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