It is composed of a single t-tubule paired with a terminal cisterna of the sarcoplasmic reticulum.

In cardiac muscle, adjacent to the intercalated disks, one would find a diad which consists of a T-tubule adjacent to a single terminal cisterna.

In cardiac muscle, the T-tubule membrane is normally opposed to a single terminal cisterna, which may wrap around the T-tubule.

In the histology of skeletal muscle, a triad is the structure formed by a T tubule with a sarcoplasmic reticulum (SR) known as the terminal cisterna on either side.