Page 302 - Atlas of Histology with Functional Correlations

(5) with its organelles. Each muscle fiber (2) consists of individual myofibrils

(8) that are arranged longitudinally. Myofibrils (8) are best seen in cross sections
of the skeletal muscle fibers in Figure 8.3. Surrounding each skeletal muscle
fiber (2) is a thin connective tissue endomysium (9), with fibrocytes (3, 6), and
capillaries (7) with blood cells.

The cross-striations of skeletal muscle fibers are the light-staining I bands

and dark-staining A bands. Each A band is bisected by the lighter H band and
the darker M band. Crossing the central region of each I band is a distinct,
narrow Z line. The filamentous and cellular segments between the Z lines
represent a sarcomere, the structural and functional unit of striated muscles

(skeletal and cardiac). When the myofibrils (8) are separated from the muscle
fiber (2), the A, I, and Z lines remain visible. The close longitudinal arrangement
of parallel myofibrils gives the skeletal muscle fibers their characteristic striated
appearance. A direct comparison with the ultrastructural image of the myofibrils

is presented in the next figure.

FIGURE 8.4 ■ Skeletal muscle fibers (longitudinal section). Stain: hematoxylin
and eosin. Plastic section. High magnification.

FIGURE 8.5 | Ultrastructure of Myofibrils in

Skeletal Muscle

To compare the light microscope illustration of Figure 8.4, an ultrastructure

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