Multiple Choice More than one choice may apply. Compare these images of a relaxed skeletal muscle fiber and a fully contracted muscle fiber. Which would you see only in the relaxed fiber? a. Z discs b. Sarcomeres c. I bands d. A bands e. H zones

Verified step by step guidance

1. Identify the structural components of a skeletal muscle fiber: Z discs, sarcomeres, I bands, A bands, and H zones.
2. Understand the changes that occur in these components during muscle contraction.
3. Recall that during contraction, the sarcomere shortens, and the I bands and H zones become narrower or disappear.
4. Recognize that the A band remains the same length during contraction.
5. Determine which components are visible only in the relaxed state by considering which ones change or disappear during contraction.

Key Concepts

Skeletal Muscle Structure

Skeletal muscle fibers are composed of myofibrils, which are further divided into sarcomeres. Each sarcomere contains specific regions that are visible under a microscope, including Z discs, I bands, A bands, and H zones, which play crucial roles in muscle contraction and relaxation.

Sarcomeres

Sarcomeres are the basic contractile units of skeletal muscle, defined by the area between two Z discs. They contain overlapping thick (myosin) and thin (actin) filaments, which slide past each other during contraction, altering the appearance of various bands and zones within the sarcomere.

Muscle Fiber Relaxation

In a relaxed muscle fiber, certain structural features are more prominent, such as the I bands and H zones. The I band is the region containing only thin filaments, while the H zone is the area within the A band where there are no thin filaments, making these features distinct in a relaxed state compared to a contracted muscle.