Answer:
The correct answer is B: "The contraction of skeletal muscles is based on myosin cross-bridges binding to actin and undergoing a power stroke".
Step-by-step explanation:
In rest, attraction strengths between myosin and actin filaments are inhibited by the tropomyosin. At this point, tropomyosin is obstructing binding sites for myosin on the thin filament. When the muscle fiber membrane depolarizes, it provokes the calcium release from the sarcolemma to the cytoplasm. Calcium ions bind to the troponin C, the troponin T alters the tropomyosin by moving it and then unblocks the binding sites. Myosin heads bind to the uncovered actin-binding and form cross-bridges. Filaments slide impulsed by chemical energy collected in myosin heads and undergo a power stroke. The power stroke initiates when the myosin cross-bridge binds to actin. Z-bands are then pulled toward each other, thus shortening the sarcomere and the I-band, and producing muscle fiber contraction.