Sliding filament theory

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Sliding filament theory

  1. 1. Sliding Filament Theory Lloyd Dean How Muscles Contract
  2. 2. Structure of Skeletal Muscle <ul><li>Epimysium </li></ul><ul><ul><li>Surrounds entire muscle </li></ul></ul><ul><li>Perimysium </li></ul><ul><ul><li>Surrounds bundles of muscle fibers </li></ul></ul><ul><li>Endomysium </li></ul><ul><ul><li>Surrounds individual muscle fibers </li></ul></ul>
  3. 3. Structure of Skeletal Muscle: Microstructure <ul><li>Sarcolemma </li></ul><ul><ul><li>Muscle cell membrane </li></ul></ul><ul><li>Myofibrils </li></ul><ul><ul><li>Threadlike strands within muscle fibers </li></ul></ul><ul><ul><li>Actin (thin filament) </li></ul></ul><ul><ul><ul><li>Troponin </li></ul></ul></ul><ul><ul><ul><li>Tropomyosin </li></ul></ul></ul><ul><ul><li>Myosin (thick filament) </li></ul></ul><ul><li>Further divisions of </li></ul><ul><li>Myofibrils </li></ul><ul><ul><li>Z-line </li></ul></ul><ul><ul><li>A-band </li></ul></ul><ul><ul><li>I-band </li></ul></ul><ul><li>Sarcoplasm </li></ul><ul><ul><li>Sarcoplasmic reticulum </li></ul></ul><ul><ul><ul><li>Storage sites for calcium </li></ul></ul></ul><ul><ul><ul><li>Surrounds myofibrils </li></ul></ul></ul><ul><ul><li>Transverse tubules </li></ul></ul>
  4. 7. Muscular Contraction <ul><li>The sliding filament model </li></ul><ul><ul><li>Muscle shortening occurs due to the movement of the actin filament over the myosin filament </li></ul></ul><ul><ul><li>Reduction in the distance between Z-lines of the Sarcomere </li></ul></ul><ul><ul><li>Lets see a preview before the play……….. </li></ul></ul>
  5. 8. Sliding Filament Theory: A Love Story <ul><li>Winner of 2 Golden Globes and 3 Oscar’s. </li></ul><ul><li>Directed by Lloyd Dean and his award winning students </li></ul><ul><li>The background </li></ul><ul><li>Actin and Myosin are in deeply in love and wish to live a happy life together and stay in full muscle contraction. </li></ul><ul><li>The nasty Tropomyosin has other idea’s……. </li></ul><ul><li>Let’s see the cast…….. </li></ul>
  6. 9. Cast <ul><li>Actin – The thin protein that needs some HELP to join with Myosin </li></ul><ul><li>Myosin - The thick protein </li></ul><ul><li>Acetylcholine – A helping hormone </li></ul><ul><li>Troponin – Will assist in removing the horrid tropomyosin from actin </li></ul><ul><li>Tropomyosin – Doesn’t want actin and myosin to become attached </li></ul><ul><li>ATP – Energetic friend </li></ul><ul><li>Calcium – Will it win it’s battle against tropomyosin ? </li></ul><ul><li>Nervous Impulse - Messenger </li></ul><ul><li>Now to the chapters of this story......... </li></ul>
  7. 10. Chapters <ul><li>A Milky Message </li></ul><ul><li>Two Forces Join </li></ul><ul><li>A T iresome P ull </li></ul><ul><li>Powering Through </li></ul><ul><li>A Milky Removal </li></ul>
  8. 11. A Milky Message <ul><li>Nerve Impulse (Action Potential) sent via motor unit to neuromuscular junction (Place where the brain and muscle communicate) </li></ul><ul><li>Hormone (Acetylcholine) diffuses from Axon terminals in neuron </li></ul><ul><li>Sodium Ions diffuse into spaces left by Ach which cause action potential to run through the muscle fibre </li></ul><ul><li>This causes calcium ions to be released in the sarcoplasmic reticulum (Surrounds myofibrils) </li></ul>
  9. 12. Two Forces Join <ul><li>Calcium ions join with troponin </li></ul><ul><li>Causes tropomyosin to be removed from actin </li></ul><ul><li>Actin and myosin join together </li></ul>
  10. 13. A T iresome P ull <ul><li>Actin and myosin are now joined </li></ul><ul><li>Myosin pulls actin inwards slightly </li></ul><ul><li>ATP enables quick detachment of actin and myosin in preparation for power stroke </li></ul>
  11. 14. Powering Through <ul><li>ATP is broken down </li></ul><ul><li>This enables Myosin to powerfully pull actin inwards </li></ul><ul><li>Sarcomere and distance between Z discs shortens </li></ul><ul><li>This process continues at a high rate and as long as there are calcium ions present </li></ul>
  12. 15. A Milky Removal <ul><li>Once impulse stops.... </li></ul><ul><li>Calcium Ions are sent back to sarcoplasmic reticulum </li></ul><ul><li>Tropomyosin rejoins actin </li></ul><ul><li>Sarcomere and Z disc distance increase </li></ul><ul><li>Muscle is relaxed </li></ul>
  13. 16. All or None Law <ul><li>Fiber contracts completely or not at all </li></ul>

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