[1][2] It consists of a lipid bilayer and a thin outer coat of polysaccharide material (glycocalyx) that contacts the basement membrane.

The basement membrane contains numerous thin collagen fibrils and specialized proteins such as laminin[3] that provide a scaffold to which the muscle fibre can adhere.

[4] It acts as a barrier between the extracellular and intracellular compartments, defining the individual muscle fibre from its surroundings.

The lipid nature of the membrane allows it to separate the fluids of the intra- and extracellular compartments, since it is only selectively permeable to water through aquaporin channels.

A transverse tubule surrounded by two SR cisternae are known as a triad, and the contact between these structures is located at the junction of the A and I bands.