skeletal muscle contraction muse. bone perimysium endomysium (between individual muscle fibers)...
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Skeletal Muscle Contraction
Muse
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Bone
Perimysium
Endomysium(between individualmuscle fibers)
Muscle fiber
Fascicle(wrapped by perimysium)
Epimysium
Tendon
Epimysium
Muscle fiberin middle ofa fascicle
Blood vessel
Perimysium
Endomysium
Fascicle(a)
(b)
Muscle cells are composed of many long fibers
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NucleusLight I bandDark A band
Sarcolemma
Mitochondrion
(b) Diagram of part of a muscle fiber showing the myofibrils. Onemyofibril is extended from the cut end of the fiber.
Myofibril
Cells are polynucleate and surrounded by sarcolemma
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Skeletal Muscle Fibers
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The overlap of fiber elements causes the striated
appearance
Z disc Z disc
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The Sarcomere
• Smallest contractile unit (functional unit) of a muscle fiber
• The region of a myofibril between two successive Z discs
• Composed of thick and thin myofilaments made of contractile proteins
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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.
Z disc Z discM line
Sarcomere
Thin (actin)filament
Thick(myosin)filament
Elastic (titin)filaments
(d) Enlargement of one sarcomere (sectioned lengthwise). Notice the myosin heads on the thick filaments.
Positions of the fibers relative to each other
Thin filaments = actin Thick filaments = myosin
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Actin is partially covered by tropomysosin
Actin
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Myosin thick filament
Myosin is a tree of heads
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10_10The signal to contract
Action potential arrives at neuromuscular junction.
acetocholine released
ligand gated sodium channels open and action potential continues along sarcolemma
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Figure 9.11, step 3
Steps inE-C Coupling:
Terminal cisterna of SR
Voltage-sensitivetubule protein
T tubule
Ca2+
releasechannel
Ca2+
Sarcolemma
Action potential ispropagated along thesarcolemma and downthe T tubules.
1
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Myofibril
Myofibrils
Triad:
Tubules ofthe SR
Sarcolemma
Sarcolemma
Mitochondria
I band I bandA band
H zone Z discZ disc
Part of a skeletalmuscle fiber (cell)
• T tubule• Terminal
cisternaeof the SR (2)
M line
Sarcoplasmic reticulum releases Ca2+
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The Contraction Cycle
• Five Steps of the Contraction Cycle
– Exposure of active sites on actin
– Formation of cross-bridges
– Pivoting of myosin heads
– Detachment of cross-bridges
– Reactivation of myosin
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The length of the sarcomere shrinks as the filaments undergo the contraction cycle
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Cross bridge detachment requires ATP hydrolysis
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Once detached, residual energy from detachment re-cocks myosin head
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Tension builds quickly
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10_11
review
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Repeated action potentials lead to maximum tension
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Different fiber types can be fast or slower to develop full
tension
.
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10_12
Metabolic sources of energy for muscle contraction