There are two types of endoplasmic reticulum cisternae. Removal of mannose residues and addition of N-acetylglucosamine occur in medial cisternae. Periodically, it has dilated end sacs known as terminal cisternae. Addition of galactose and sialic acid occurs in the "trans" cisternae. There are several mechanisms directly linked to the terminal cisternae which facilitate Excitation-Contraction coupling. However, research shows that the reticulons are restricted to the edges of the ER cisternae. Together, two terminal cisternae and a transverse tubule form a triad. The general structure of the endoplasmic reticulum is a network of membranes called cisternae. The functions of cisternae change as it undergoes micromaturation. Cisternae pack and modify proteins and polysaccharides. T-tubules in skeletal muscle are associated with two terminal cisternae, known as a triad. However, as the parasite ages Maurer's clefts expand to form single flattened cisternae, 500-nanometers wide. Almost all cisternae in the Golgi apparatus exhibit multiple stacking. In between two terminal cisternae is a tubular infolding called a transverse tubule (T tubule). A mammalian cell typically contains 40 to 100 stacks of cisternae.