Myofibril:A long filamentous organelle found within muscle cells that has a banded appearance and is involved in muscular contraction.
T: tubules (Transverse tubules) - Invaginations of the sarcolemma that penetrate into the cell interior and help spread electrical impulses quickly throughout the muscle fiber.
Sarcoplasmic reticulum: A specialized form of smooth endoplasmic reticulum that stores and releases calcium ions to trigger muscle contraction