2009_Book_FoodChemistry

12.2 Structure of Muscle Tissue 567
Fig. 12.3. A cross-section of
a muscle fiber. (from Schultz,
Anglemier, 1964)
Fig. 12.4. An oblique view of a fractured muscle
fiber; scanning electron microscopy at −180 ◦ C(Sargent,
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 microscopy
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 mitochondria
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-