Final answer:
The structure formed by a T tubule with a sarcoplasmic reticulum on either side in skeletal muscle is known as a triad, which functions in the conduction of electrical impulses and regulation of intracellular calcium for muscle contraction.
Step-by-step explanation:
The structure formed by a T tubule with a sarcoplasmic reticulum (SR) known as the terminal cisterna on either side found in the skeletal muscle is known as a triad. A triad is comprised of two terminal cisternae, where the enlarged SR connects to the T-tubule, and one T-tubule. This arrangement creates a 'threesome' of membranes, with the SR on two sides and the T-tubule sandwiched between them, facilitating the conduction of electrical impulses and the regulation of intracellular levels of calcium.
When an action potential propagates along the sarcolemma and enters the T-tubules, it triggers the opening of calcium channels in the membrane of the adjacent SR. The subsequent diffusion of calcium ions (Ca++) out of the SR and into the sarcoplasm initiates the contraction of muscle fibers by the contractile units known as sarcomeres.