Morphology of T-tubules and Sarcoplasmic Reticulum SARCOLEMMA- T-TUBULE MITOCHONDRION RETTOLUMMIC CISTERNA NERCORBULAR MITOCHONDRION I-BAND A-BAND Z-LINE The excitatory event is an AP that is conducted along the cell membrane.the AP is conducted along T-tubules that penetrate through the inside of the cell.The T- tubules serve to carry the excitation event directly to the Sarcoplasmic Reticulum(SR),where the cell's internal Calcium is stored. SR is a reservoir of calcium ions,surrounded by a membrane.Its walls are studded with SERCA pumps:(SERCA Sarcoplasmic Endoplasmic Reticulum Ca++ATPases)that pump Ca ions from the intracellular compartment into the SR