280
UNIT 2
Covering, Support, and Movement of the Body
9
Nuclei
Fiber
Nucleus
Light I band
Dark A band
Sarcolemma
Mitochondrion
I band
Z disc
Z disc
I band
A band
H zone
(a)
Thin (actin)
filament
Thick (myosin)
filament
Z disc
Z disc
M line
M line
Sarcomere
I band
thin filaments
only
Dark A band
Light I band
Thin (actin)
filament
Thick
(myosin)
filament
Actin
filament
Myosin
filament
Elastic (titin)
filaments
H zone
thick filaments
only
M line
thick filaments linked
by accessory proteins
Outer edge of A band
thick and thin
filaments overlap
Photomicrograph of
portions
of two isolated muscle
fibers
(700
m
). Notice the
obvious striations
(alternating dark and light
bands).
(b)
Diagram of
part of a
muscle fiber
showing
the myofibrils. One
myofibril
extends from
the cut end of the fiber.
(c)
Small part of one
myofibril enlarged to
show the myofilaments
responsible for the
banding pattern. Each
sarcomere
extends from
one Z disc to the next.
(d) Enlargement of one
sarcomere
(sectioned
lengthwise). Notice the
myosin heads on the thick
filaments.
(e) Cross-sectional view of a
sarcomere
cut through in
different locations.
Myofibril
Figure 9.2
Microscopic anatomy of a skeletal muscle fiber.
(For a related image, see
A Brief Atlas of the Human Body
, Plate 28.)
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