Final answer:
Terminal cisternae are crucial for muscle contraction as they release Ca2+ when T-tubules are depolarized by an action potential, facilitating muscle fiber contraction. This process is essential for the excitation-contraction coupling in muscle cells.
Step-by-step explanation:
Terminal cisternae are indeed important regions of the sarcoplasmic reticulum (SR) because they are closely associated with T-tubules and release calcium ions (Ca2+) during muscle contraction. The answer to the question is a) True. When an action potential depolarizes the T-tubules, it triggers the opening of calcium channels in the membrane of the adjacent SR, allowing Ca2+ to diffuse out into the sarcoplasm, which initiates the contraction of the muscle fiber.
The T-tubules allow the action potential to propagate into the interior of the muscle cell. This arrangement, known as a triad, is essential for the coordinated release of Ca2+ from the SR and the subsequent muscle fiber contraction. For these processes to occur efficiently, the structure of the T-tubule and the terminal cisternae must function in a synchronized manner.