Skeletal Muscle Structure & Contraction

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Last updated 6:28 PM on 10/4/26
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39 Terms

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Skeletal muscle
voluntary striated muscle
voluntary striated muscle
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Cardiac muscle
striated muscle
striated muscle
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Smooth muscle
non-striated muscle
non-striated muscle
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Muscle fiber
muscle cell
muscle cell
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Myofibril
long contractile structure inside a muscle fiber
long contractile structure inside a muscle fiber
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Sarcomere
basic contractile unit
basic contractile unit
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Actin
thin filament
thin filament
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Myosin
thick filament
thick filament
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Muscle organization
whole muscle → muscle fiber bundles → muscle fibers → myofibrils → sarcomeres
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Z-line

boundary of a sarcomere
boundary of a sarcomere
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A-band
region containing thick filaments
region containing thick filaments
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I-band
region containing thin filaments without thick filament overlap
region containing thin filaments without thick filament overlap
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Sliding filament mechanism
actin and myosin slide past each other
actin and myosin slide past each other
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Muscle contraction
sarcomeres shorten because actin slides toward the center
sarcomeres shorten because actin slides toward the center
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Troponin
binds Ca²⁺
binds Ca²⁺
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Tropomyosin
blocks actin binding sites
blocks actin binding sites
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Cross-bridge
connection between myosin and actin
connection between myosin and actin
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Cross-bridge cycle

myosin binds actin → pulls → releases (ATP needed) → repeats

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Neuromuscular junction
nerve-muscle connection
nerve-muscle connection
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Acetylcholine
activates the muscle fiber
activates the muscle fiber
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Nicotinic ACh receptor
receptor activated by acetylcholine
receptor activated by acetylcholine
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Sarcoplasmic reticulum
stores Ca²⁺
stores Ca²⁺
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Ca²⁺-ATPase
pumps Ca²⁺ back into the SR
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Excitation-contraction coupling
links electrical muscle activation to contraction
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Muscle activation sequence
motor neuron → ACh release → muscle fiber activation → Ca²⁺ release → Ca²⁺ binds troponin → tropomyosin moves → myosin binds actin → contraction
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Muscle relaxation
Ca²⁺ is taken back up into the SR
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Curare poisoning
prevents ACh from activating skeletal muscle
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Rigor mortis
muscle stiffness after death because ATP is no longer available for normal cross-bridge cycling
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Creatine phosphate
rapid ATP supply
rapid ATP supply
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Glycolysis
breaks down glucose
breaks down glucose
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Oxidative phosphorylation
produces ATP using oxygen
produces ATP using oxygen
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Lactic acid
associated with glycolysis
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Myosin-ATPase
uses ATP during cross-bridge cycling
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Ca²⁺-ATPase
uses ATP to pump Ca²⁺ back into the SR
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Contraction ATP use

45–75%

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Activation ATP use
20–50%
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Protein Synthesis (basal) ATP use

5–10%
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Type I fibers (slow-oxidative fibers)

smaller + highly resistant to fatigue + slow contraction time

<p>smaller + highly resistant to fatigue + slow contraction time</p>
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Type II fibers (fast-glycolytic fibres)

larger + fatigable + fast contraction time

<p>larger + fatigable + fast contraction time </p>