Food Chemistry

12.2 Structure of Muscle Tissue 567

Fig. 12.3.A cross-section of
a muscle fiber. (fromSchultz,
Anglemier, 1964)

Fig. 12.4.An oblique view of a fractured muscle
fiber; scanning electron microscopy at− 180 ◦C(Sar-
gent, 1988)

a schematic representation of the structure of
a sarcomere derived from Fig. 12.6 and 12.7.
The thick filaments are formed from the protein
myosin. They stretch through the entire A band
and are fixed in a hexagonal arrangement by
the bulge at the center (M line) (Fig. 12.8 a,
IV). Thin filaments consist mainly of actin.
They original from the Z line, pass across the
I band and between the thick filaments, and
penetrate the A bands (Figs. 12.7 and 12.8).
During muscle contraction, the mechanism of
which is explained in section 12.3.2.1.5, the
thick filaments penetrate into the H zones and the
Z lines move closer to each other. Thus, the width
of the I band gradually decreases and finally
disappears. Figure 12.8b schematically presents

Fig. 12.5.Separated myofibrils; scanning electron mi-

croscopy at− 180 ◦C(Sargent, 1988)

these changes which take place during muscle

contraction.

12.2.2 Heart Muscle

The structure of heart muscle is similar to striated

skeletal muscle but has significantly more mito-

chondria and sarcoplasm.

12.2.3 Smooth Muscle

The smooth muscle cells are distinguished by

their centrally located cell nuclei and optically

uniform myofibrils which do not have crossstri-