A cross-sectional view of a skeletal muscle fiber through the H-zone would show the presence of:
**Core Concept**
Skeletal muscle fibers are composed of repeating units called sarcomeres, which are the functional and structural units of muscle contraction. The H-zone is a region within the sarcomere where the thick myosin filaments are located.
**Why the Correct Answer is Right**
The H-zone is a region within the sarcomere where the thick myosin filaments are located. In a cross-sectional view, the H-zone would show the presence of **myosin filaments**, which are the contractile units of the muscle. The myosin filaments are composed of the myosin head, which interacts with the actin filaments to produce muscle contraction. The myosin filaments are located in the A-band, but the H-zone specifically refers to the region where the myosin filaments are not overlapped by the actin filaments.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the I-zone (or Z-line) refers to the region where the actin filaments are attached to the sarcomere, not the thick myosin filaments.
**Option B:** This option is incorrect because the M-line (or M-band) refers to the region where the thick myosin filaments are anchored, but it does not specifically refer to the presence of myosin filaments.
**Option C:** This option is incorrect because the A-band is the region where the thick myosin filaments are located, but it is not the specific region of overlap between the actin and myosin filaments.
**Clinical Pearl / High-Yield Fact**
Understanding the structure of skeletal muscle fibers is crucial for diagnosing muscle disorders. The H-zone is an important region to understand in the context of muscle pathology, where changes in the H-zone can indicate muscle disease or injury.
**Correct Answer: C. Myosin filaments**