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The Myofibril
The Myofibril
Each muscle fiber (muscle cell) is made up of rod like myofibrils that run parallel to the length of the muscle fiber.
They contain the contractile elements of the muscle.
The Myofibril
Myofibrils
The myofibrils number in the hundreds to the thousands in a single muscle fiber.
Myofibrils
The myofibrils number in the hundreds to the thousands in a single muscle fiber.
They make up 80% of the cell volume.
Myofibrils
The myofibrils number in the hundreds to the thousands in a single muscle fiber.
They make up 80% of the cell volume.
The myofibrils are made up of smaller rod like structures called myofilaments.
Myofibrils
Examination of a muscle fiber will show a series of dark and light bands which create the striations seen in skeletal muscle
Myofibrils
These striations are produced by the myofilaments which make up the myofibrils.
Myofibrils
The dark bands are called A bands and the light bands, the I bands.
Myofibrils
These striations are created by the myofilaments actin and myosin.
These are the contractile elements of the muscle.
Myofibrils
These striations are created by the myofilaments actin and myosin.
Actin filaments are called the thin fibers and make up the I band.
Myofibrils
These striations are created by the myofilaments actin and myosin.
Actin filaments are called the thin fibers and make up the I band.
Myosin filaments are called the thick fibers and make up the A band.
Myofibrils
Myofibrils
Myofibrils
The dark A band has a lighter zone in it called the H zone.
Each H zone is bisected by a dark line called the M line.
Myofibrils
The I bands are lighter and have a midline dark band called the Z band.
The Z band is used to define the functional unit called the sarcomere.
The Sarcomere
Because muscle fibers are very long, they are divided up into small contractile units called the Sarcomere.
It averages 2 micrometers and is the distance between two successive Z discs
I band I bandA bandSarcomere
H zoneThin (actin)filament
Thick (myosin)filament
Z disc Z disc
M line
Actin
The thin filaments contain actin extend across the I band and part way into the A band. The Z disc anchors the thin filaments.
Actin and Myosin
Myosin makes up the thick filament.
The M line is formed by myosin molecules that are linked together.
Copyright © 2010 Pearson Education, Inc.
Figure 9.2c Microscopic anatomy of a skeletal muscle fiber.
I band I bandA bandSarcomere
H zoneThin (actin)filament
Thick (myosin)filament
Z disc Z disc
M line
(c) Small part of one myofibril enlarged to show the myofilamentsresponsible for the banding pattern. Each sarcomere extends fromone Z disc to the next.
Copyright © 2010 Pearson Education, Inc.
I bandthin
filamentsonly
Actinfilament
Myosinfilament
H zonethick
filamentsonly
M linethick filaments
linked byaccessoryproteins
Outer edgeof A band
thick and thinfilaments overlap
(e) Cross-sectional view of a sarcomere cut through in different locations.
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