T tubule system, a system of tubular invaginations along the surface of all striated muscle cell membranes, providing an extension of the membrane into the cells. The system is believed to be part of an extensive endomembrane system involved in storing calcium ions and in the movement of action potentials into the cells. T tubules are likely to be the link between membrane stimulation and the triggering of the release of calcium ions from the sarcoplasmic reticulum.
