Which of the following best describes muscle B compared with muscle A?: (A) Adapted for rapid contraction, (B) Composed of larger muscle fibers, (C) Fewer mitochondria, (D) Innervated by smaller nerve fibers
Answer is D. Muscle B is characteristic of a slow-twitch muscle (type 1) composed of predominantly slow-twitch muscle fibers. These fibers are smaller in size and are innervated by smaller nerve fibers. They typically have a more extensive blood supply, a greater number of mitochondria, and large amounts of myoglobin, all of which suppo high levels of oxidative phosphorylation.