sliding filament model of muscle contraction
DESCRIPTION
HOOK Muscle is only biological cell/tissue that can cause rapid, large-scale movement Role of filamentous proteins understood as great and early breakthrough in cell/molecular biology—lots of protein available, (like Hemoglobin). Sliding Filament Model of Muscle Contraction. - PowerPoint PPT PresentationTRANSCRIPT
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Sliding Filament Model of Muscle Contraction
Larry M. Frolich, Ph.D.April 15, 2010
HOOK• Muscle is only biological
cell/tissue that can cause rapid, large-scale movement
• Role of filamentous proteins understood as great and early breakthrough in cell/molecular biology—lots of protein available, (like Hemoglobin)
I normally cover neurons and muscle together as part of unit on movement—see website
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Sliding Filament Model of Muscle Contraction
OUTLINE Motor Unit Muscle Cell Architecture
and Function Sliding Filamentous
Proteins Muscle Force Properties
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Muscle Cells and Neurons• are unique to animals• have “excitable”
membranes that transmit action potentials
• allow for rapid large-scale movements
• Motor Unit is one motor neuron plus the muscle cells that it stimulates (or synapses with)--the minimal construct that allows for movement in our body
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• Muscle fibers are cells—visible to naked eye as fibers in meat, chicken, fish
• Sarcolemma is muscle cell membrane—”excitable” so has action potentials just like neurons
• Because cell is large, T-tubules carry action potential—ionic depolarization—into internal parts of cell
• Sarcoplasmic reticulum releases calcium which triggers actin-myosin protein filaments to contract
Muscle cells
Sequence of events Motor Neuron to Muscle contraction at cellular level (from the Brain Top to Bottom) [link]
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Muscle cell or muscle “fiber” is composed of myofibrils which contain sarcomeres or contractile “units”
Myo-Sarco-(= muscle)
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Molecular Basis of Muscle Function
• Actin-Myosin “sliding filament” model
• Explains– Muscle movement
or shortening– Muscle force
generation or “contraction”
• Actin and myosin filamentous proteins are packed parallel in sarcomeres
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How does the actin-myosin complex (sarcomere) shorten and contract the muscle?
• Actin = thin filament “lattice-work”
• Myosin = thick filament “core”
• Ca release triggers the formation of molecular cross-bridges from myosin to actin
• Cross-bridges “row” or “reach” for more adjacent binding site on actin.
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Put the
slidi
ng fil
amen
ts ba
ck in
to a w
hole
muscle
…
And the result is muscle movement
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Details, details, details…
• Tropomyosin and troponin create binding site on actin filament
• Presence of Ca++ exposes binding site
• “Cocked” cross-bridge on myosin (uses ATP) then attaches to binding site and pulls or “rows” actin filament
• Cross-bridge linkage is broken and re-cocks to link with next binding site
Details Video
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Sliding Filament Model explains• Why muscle has peak force at
certain length: (ideal actin-myosin overlap for cross-bridge formation)—BUCKET DEMO
• More muscle cells means more muscle force: (more cross-bridge formation)—EMG, Isolated muscle online lab
• Concentric/isometric/eccentric contraction: Cross-bridges continue to form and “reach” even if opposing force is greater