Talk about the sarco-tubular system of the cardiac muscle cell.

The sarco-tubular system of myocardiac cells differs from that of skeletal striated cells. The sarcoplasmic reticulum is less developed than that of the skeletal striated muscle cells. It is formed of longitudinal tubules (L tubules) and extends between myofilaments and beneath the sarcolemma and does not contain a triad. The T tubules of the cardiac cell are more numerous and larger in diameter than those of the skeletal fiber, they invaginate at the Z-line level of myofibrils, not at the A- I junction level. Every T tubule is generally associated to an L tubule, and together they form a dyad.