This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Name the structure that is NOT involved in excitation-contraction coupling in striated muscle: 
Select and explain. 
A. Microtubules, B. Sarcolemma, C. Sarcoplasmic Reticulum, D. Motor end plate
A: Microtubules
Answer: A: Microtubules 
Explanation: Microtubules play no role in excitation-contraction coupling. Action potentials are propagated by the sarcolemma as an essential step in excitation-contraction coupling. Ca++ release from the sarcoplasmic reticulum is necessary for excitation-contraction coupling. The motor end plate is the site of neuromuscular transmission, the first stage of excitation-contraction coupling. T-tubules provide an electrical link whereby action potentials trigger Ca++ release from the sarcoplasmic reticulum.