Page 321 - Atlas of Histology with Functional Correlations

FIGURE 8.17 | Ultrastructure of Smooth Muscle

Fibers from Section of Intestinal Wall

In comparing the ultrastructure of the skeletal (see Figs. 8.5 and 8.6) and cardiac
(see Fig. 8.13) muscle fibers with smooth muscle fibers, there is a significant

difference in their internal morphology. The orderly arrangement of actin and
myosin that gave skeletal and cardiac muscles a striated appearance is absent.
Although individual filaments are visible in the cell cytoplasm (4), their

arrangement is random. The thin actin filaments attach to the dense bodies (1, 5)
at the cell membrane (1, 5) or to dense bodies (6, 9) scattered in the cytoplasm
(4) of smooth muscle cell (4). The dense bodies (1, 5, 6, 9) are functionally
similar to the Z discs of the skeletal and cardiac muscles. The numerous
invaginations along muscle cell membranes are the caveolae (arrows). Within

the cell cytoplasm (4) are also seen a mitochondrion (8) and remnants of the
sarcoplasmic reticulum (7). Smooth muscle cytoplasm (4) is surrounded by
basal lamina (3), and between individual smooth muscle fibers, there are

collagen fibers of the connective tissue (2, 10).

FIGURE 8.17 ■ Ultrastructure of smooth muscle fibers from a section of an
intestinal wall. Courtesy of Dr. Rex A. Hess, Professor Emeritus Comparative
Biosciences, College of Veterinary Medicine, University of Illinois, Urbana, IL.

Approximately ×10,500.

FUNCTIONAL CORRELATIONS 8.4 ■ Smooth

Muscle

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