Triad
In skeletal muscle, a triad is formed when a T-Tubule is flanked on either side by the calcium containing Terminal Cisternae of the Sarcoplasmic Reticulum, at the level of the Z-line. The intimate association of these three membranous sturctures (Terminal Cisternae---T-Tubule---Terminal Cisternae) for a Triad. This differs from a diad (or Dyad), in cardiac muscle where the T-Tubule is only intimately associated with ONE Terminal Cisternae.
Triad
Two terminal cisternae and a T-tubule
It is the terminal cisternae
one transverse tubule and two terminal cisternae
action potential propagating down the T tubule
The Sarcoplasmic Reticulum stores calcium and releases it through the terminal cisternae into the tubule.
The enlarged portion of sarcoplasmic reticulum on either side of a transverse tubule is called a terminal cisterna. These terminal cisternae play a vital role in the excitation-contraction coupling of skeletal muscle cells. They store and release calcium ions, which are essential for muscle contraction.
I believe the T-Tubule
The Sarcoplasmic Reticulum stores calcium and releases it through the terminal cisternae into the tubule.
Papillary Duct
Proximal Convoluted Tubule