Final answer:
The T-tubule is flanked by two terminal cisternae of the sarcoplasmic reticulum, facilitating the opening of ryanodine receptors that release calcium ions to initiate muscle contraction.
Step-by-step explanation:
In the T-tubule triad structure of striated muscle observed in electron micrographs, the T tubule is flanked by two terminal cisternae of the sarcoplasmic reticulum (SR). This anatomical setup is critical for muscle contraction, as it facilitates the opening of ryanodine receptors on the terminal cisternae. When an action potential reaches the T-tubules, these calcium channels are triggered to open, causing calcium ions (Ca2+) to be released into the sarcoplasm. The increase in Ca2+ concentration initiates the contraction of the muscle fiber by causing the actin and myosin filaments within the sarcomeres to interact, leading to muscle contraction.
In the T-tubule triad structure seen in electron micrographs of striated muscle, the T tubule is flanked by two terminal cisternae of the sarcoplasmic reticulum (SR). This association facilitates opening terminal cisternae ryanodine receptors, which release calcium ions (Ca2+) to initiate sarcomere contraction.