Biomedical Engineering Reference
In-Depth Information
Fasciculus
or fascicle
Epimysium
Perimysium
Endomysium
Axon of
motor neuron
Skeletal muscle
Blood capillary
Sarcolemma
Muscle fibers (cells)
Blood vessels
(a) Entire skeletal muscle
(b) Several fasciculi (fascicles)
Muscle fiber (myofiber)
Nucleus
Nuclei
Sarcoplasmic
reticulum
Satellite cell
Mitochondrion
Sarcolemma
Triad
Sarcoplasm
Transverse
tubule
Te r minal
cistern
(c) Muscle
fiber
(myofiber)
Sarcolemma
Myofibril
Z disc
Crossbridge
(d) Several myofibrilis
hin filament (actin)
hick filament (myosin)
Z disc
(e) hick and thin filaments (mvofilaments)
FIGURE A.4
Skeletal muscle structure.
The two contractile proteins in muscle are myosin and actin. About 200 mole-
cules of the protein myosin form a single thick filament. Each myosin molecule is
shaped like two golf clubs twisted together. The tails (golf club handles) point toward
the M-line in the center of the sarcomere. The projecting myosin heads, called cross-
bridges, extend out toward the thin filaments. Tails of the neighboring myosin
molecules lie parallel to one another, forming the shaft of the thick filament. The
heads project from all around the shaft in a spiraling fashion.
Thin filaments extend from anchoring points within the Z-discs. Their main
component is actin. In addition, smaller amounts of two regulatory proteins, tro-
pomyosin and troponin, are present in the thin filament. Individual actin molecules
