This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Membrane Potentials and Action Potentials, Subject name: Physiology
Action potential is transmitted in myofibrils via: 
Select and explain. 
A. Terminal cisterns, B. T- Tubules, C. Longitudinal, D. Sarcomere
B: T- Tubules
Answer: B: T- Tubules 
Explanation: Ans: B (T- Tubules) Ref: Pal GK. Muscle, In: Textbook of Medical Physiology, Ahuja Publishing House 2007: 20:177Explanation:T-Tubules are tubular extensions of sarcolemma. that penetrate to the center at the junctions of A and I bands. It is involved in conduction of action potential from NMJ to the triad formed by terminal cisternae and L tubules (part of sarcotubular system).Terminal cisternae - dilated region at both ends of elongated tubules (L-tubules), a part of Sarcoplasmic reticulum - involved in calcium release.* Sarcomere - structural functional unit of myofibril; portion of myofibril between two successive Z lines.