sliding filament theory
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Sliding Filament Theory
Lloyd Dean
How Muscles Contract
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Structure of Skeletal Muscle
EpimysiumSurrounds entire muscle
PerimysiumSurrounds bundles of muscle fibers
EndomysiumSurrounds individual muscle fibers
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Structure of Skeletal Muscle:MicrostructureSarcolemma
Muscle cell membrane
MyofibrilsThreadlike strands
within muscle fibersActin (thin filament)
TroponinTropomyosin
Myosin (thick filament)
Further divisions ofMyofibrils
Z-lineA-bandI-band
SarcoplasmSarcoplasmic
reticulumStorage sites for
calciumSurrounds myofibrils
Transverse tubules
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Muscular ContractionThe sliding filament model
Muscle shortening occurs due to the movement of the actin filament over the myosin filament
Reduction in the distance between Z-lines of the Sarcomere
Lets see a preview before the play………..
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Sliding Filament Theory:A Love Story
Winner of 2 Golden Globes and 3 Oscar’s.Directed by Lloyd Dean and his award winning
students
The backgroundActin and Myosin are in deeply in love and wish to
live a happy life together and stay in full muscle contraction.
The nasty Tropomyosin has other idea’s…….
Let’s see the cast……..
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Cast Actin – The thin protein that needs some HELP to join with
Myosin
Myosin - The thick protein
Acetylcholine – A helping hormone
Troponin – Will assist in removing the horrid tropomyosin from actin
Tropomyosin – Doesn’t want actin and myosin to become attached
ATP – Energetic friend
Calcium – Will it win it’s battle against tropomyosin?
Nervous Impulse - Messenger
Now to the chapters of this story.........
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Chapters1. A Milky Message
2. Two Forces Join
3. A Tiresome Pull
4. Powering Through
5. A Milky Removal
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A Milky Message Nerve Impulse (Action Potential)
sent via motor unit to neuromuscular junction (Place where the brain and muscle communicate)
Hormone (Acetylcholine) diffuses from Axon terminals in neuron
Sodium Ions diffuse into spaces left by Ach which cause action potential to run through the muscle fibre
This causes calcium ions to be released in the sarcoplasmic reticulum (Surrounds myofibrils)
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Two Forces JoinCalcium ions join
with troponin
Causes tropomyosin to be removed from actin
Actin and myosin join together
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A Tiresome PullActin and myosin
are now joined
Myosin pulls actin inwards slightly
ATP enables quick detachment of actin and myosin in preparation for power stroke
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Powering ThroughATP is broken down
This enables Myosin to powerfully pull actin inwards
Sarcomere and distance between Z discs shortens
This process continues at a high rate and as long as there are calcium ions present
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A Milky RemovalOnce impulse stops....
Calcium Ions are sent back to sarcoplasmic reticulum
Tropomyosin rejoins actin
Sarcomere and Z disc distance increase
Muscle is relaxed
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All or None Law
Fiber contracts completely or
not at all
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