Muscle cell (myocyte, muscle fiber) anatomy:
Sarcoplasmic reticulum: specialized area of the endoplasmic reticulum
Surrounds the myofibrils like a web
At each end, forms bag-like structure “terminal cisternae”
Area where calcium (Ca2+) is stored
Transverse tubules: tube formation of the sarcolemma
Tubes run from the external surface straight through the muscle cell
Transverse tubules and terminal cisternae form a “triad” structure (many of these along the length of the muscle cell)