Final answer:
The sarcomere shows a striation pattern under a light microscope, comprised of A bands with overlapping actin and myosin, I bands with actin, Z lines demarcating each sarcomere, an H zone with myosin only, and an M line in the H zone's center.
Step-by-step explanation:
The sarcomere is the functional unit of a muscle fiber, and under a light microscope, it presents a distinctive striation pattern within a myofibril. The pattern seen consists of dark and light bands: the A band appears dark and includes overlapping thick (myosin) and thin (actin) filaments. In the center of the A band is a lighter region called the H zone, where there is no overlap of actin filaments. The I band appears light and contains primarily thin filaments (actin). Each sarcomere is demarcated by Z lines (or Z-discs), which anchor the actin filaments. Finally, the center of the H zone is crossed by the M line, which holds the myosin filaments together. The regular arrangement of these structures causes the striated pattern visible in skeletal muscle fibers.