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Structure of Skeletal Muscles
Types of Muscles
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striated feature |
voluntary contraction |
examples |
| skeletal muscles |
yes |
yes |
extremity muscles |
| cardiac muscles |
yes |
no |
heart |
| smooth muscles |
no |
no |
internal organs |
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Some statistics about skeletal muscles
the most abundant tissue in the body, accounting for 40-45% of total BW
> 430 skeletal muscles
Most movements are completed by < 80 pairs of skeletal muscles
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Properties of skeletal muscles
muscle fiber
extensibility
elasticity
contractility
tendon or aponeurosis
viscoelasticity
non-contractility
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Organization of skeletal muscles
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epimyosium
muscle¡G
contractile elements that are embedded within a network of connective tissues
perimyosium
fasciculus
endomyosium
sacrolemma
muscle fiber
myofibril
myosin
actin
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Muscle fibers
a long cylindrical cell with hundreds of nuclei
10-100 mm in diameter
1-30 cm in length
contractile component: myofabril
non-contractile component: endomyosium
types
slow twitch fiber (type I)
red in color because of abundant blood supply
slower to the peak when contracted
fatigue resistant
fast twitch fiber (type IIA)
pale in color because of less blood supply
rapidly to the peak when contracted
easy fatigue
intermediate fiber (type IIB)
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Skeletal muscle architecture
parallel fiber arrangement¡G
parallel to the longitudinal axis of the muscle
longitudinal¡G sartorius
quadrate or quadralateral¡G rhomboid
triangular or fan-shaped¡G pectoralis major
fusiform or spindle-shaped¡G biceps brachii
pennate fiber arrangement¡G
at an angle to the longitudinal axis of the muscle
unipenniform¡G extnesor digitorum longous
bipenniform¡G flexor hallucis longus
multipenniform¡G middle fibers of the deltoid
Note¡G Lieber RL(1992) divided skeletal muscle architecture into 3 general types
longitudinal architecture¡G biceps brachii
unipennate architecture¡G vastus lateralismultipennate architecture¡G
gluteus medius
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effect of the angle of pennation
the greater the angle of pennation, the smaller the amount of effective force transmitted to the tendon
the angle of the pennation increases as tension progressively increases in the muscle fibers
The pennate arrangement will allow the packing of more fibers given the same space.
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