Page 313 - Atlas of Histology with Functional Correlations

skeletal muscle fibers. Surrounding the nucleus of a cardiac muscle fiber is a

prominent perinuclear sarcoplasm (2, 10) that is devoid of cross-striations and
myofibrils.

The connective tissue fibrocytes (6, 8) and the fine connective tissue fibers
of endomysium (4) surround the cardiac muscle fibers. Capillaries with
erythrocytes (11) are normally seen in the endomysium (4, 6, 8).

FIGURE 8.12 ■ Cardiac muscle in longitudinal section. Stain: hematoxylin and
eosin. High magnification.

FIGURE 8.13 | Ultrastructure of Cardiac Muscle

in Longitudinal Section

This ultrastructure image illustrates the internal structures of cardiac muscle
fiber. A distinct sarcomere (1) with regular arrangements of thin actin and thick
myosin filaments is located between the dense-staining Z lines (3). Visible in the
sarcomere (1) is the denser A band (2) containing both actin and myosin

filaments and the light-staining I band (8) with actin filaments that are bisected
by the Z lines (3). Located between the myofibrils are the large mitochondria
(4) that are characteristic of cardiac muscle. In contrast to skeletal muscle, the
sarcoplasmic reticulum (5) is not as well organized and exhibits only small

terminal cisternae. Also, cardiac muscles exhibit only one T tubule (9) per
sarcomere, seen at the level of the Z line (3). In the middle of the sarcomere (1)
are darker M bands (7) bands that represent the linkages of the thick myosin
filaments. A highly characteristic feature of the cardiac muscle fibers is the

dense-staining intercalated disc (6) with its irregular, zigzag pattern that crosses
the cardiac muscle fibers. These discs represent important attachment sites

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