Definition for Terminal cisternae
From Biology Forums Dictionary
Terminal cisternae are enlarged areas of the sarcoplasmic reticulum surrounding the transverse tubules. These discrete regions within the muscle cell store calcium (increasing the capacity of the sarcoplasmic reticulum to release calcium) and release it when an action potential courses down the transverse tubules, eliciting muscle contraction. Because terminal cisternae ensure rapid calcium delivery, they are well developed in muscles that contract quickly, such as fast twitch skeletal muscle. The T-tubules plus adjacent terminal cisternae create a triad. 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.
Terminal cisternae are pairs of transversely oriented tubules of the sarcoplasmic reticulum occurring at regular intervals in skeletal muscle fibers; together with an intermediate T tubule they make up a triad.