Muscle
Tendon
Muscle fiber
(a single
muscle cell)
Muscle
fiber
Dark A band
Light I band
Myofibril
Connective
tissue
(a) Relationship of a whole muscle and a muscle fiber
M line
(b) Relationship of
a muscle fiber and
a myofibril
Z line
A band
Thick
Cross Thin
bridge filament filament
I band
Portion of
myofibril
H zone
Thick
filament
Thin
filament
(c) Cytoskeletal
components of
a myofibril
M line
Actin
Cross bridges
A band
I band
H zone
Z line
Z line Titin Thin filament M line
Myosin head
Myosin tail
Sarcomere
Thick filament
Z line
Thick filament
Troponin
Tropomyosin
Thin filament
(d) Protein components of
thick and thin filaments
(e) The highly elastic protein titin
❙ Figure 8-2 Levels of organization in a skeletal muscle. Note in part (c) in the cross section of a myo bril through the A band where thick and thin laments overlap
that each thick lament is surrounded by six thin laments and each thin lament is surrounded by three thick laments.
FIGURE FOCUS: How would a cross section through the H zone (outside of the M line) and one through the I band (outside of the Z line) differ from
the cross section through the A band (outside of the H zone) shown in part (c)?
Unless otherwise noted, all content on this page is © Cengage Learning.
Muscle Physiology
253