This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Skeletal Muscle: Contraction and Excitation, Subject name: Physiology
[{'content': 'Band not covered by actin filament is? \nSelect and explain. \nA. H band, B. I band, C. M band, D. Z band', 'role': 'user'}, {'content': "Answer: A \nExplanation: ANSWER: (A) H bandREF: Ganong's 22nd ed* The area between two adjacent Z lines is called a sarcomereThe thick filaments, which are about twice the diameter of the thin filaments, are made up of myosin; the thin filaments are made up of actin, tropomyosin and troponinThe thick filaments are lined up to form the A bands, whereas the array of thin filaments forms the less dense I bandsThe lighter H bands in the center of the A bands are the regions where, when the muscle is relaxed, the thin filaments do not overlap the thick filamentsThe Z lines transect the fibrils and connect to the thin filaments. If a transverse section through the A band is examined under the electron microscope, each thick filament is seen to be surrounded by six thin filaments in a regular hexagonal pattern.", 'role': 'assistant'}]