Muscle Movement

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Muscle Movement
2012-02-22 08:53:43
muscle contraction relaxation

Major events of muscle contraction and relaxation
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  1. Step One (contraction)
    nerve impluse travels down a motor neuron axon
  2. Step Two (contraction)
    motor neuron terminal releases ACh (acetylcholine neurotransmitter)
  3. Three (contraction)
    ACh binds to ACh receptors on muscle fiber
  4. Four (contraction)
    sarcolemma is stimulated, muscle impulse travels surface of muscle fiber and deep into fiber through transverse tubules

    *note: remember sarcomere is functional unit of skeletal mm, sarcolemma is muscle cell membrane
  5. Five (contraction)
    muscle impulse reaches sarcoplasmic reticulum and calcium channels open
  6. Six (contraction)
    Calcium ions diffuse from sarcoplasmc reticulum into sarcoplasm and bind to troponin molecules
  7. Seven (contraction)
    tropomyosin molecules move and expose binding sites on actin
  8. Eight (contraction)
    actin and myosin bind/link

    *note: remember actin= thin filament, myosin= thick filament
  9. Nine (contraction)
    thin (actin) filaments pulled toward center of sarcomere by myosin cross-bridges increasing the overlap of thick and thin filaments
  10. Ten (contraction)
    muscle fiber finally contracts!
  11. Step One (relaxation)
    acetylocholinesterase decomposes acetylcholine (ACh), muscle fiber membrane no longer stimulated
  12. Two (relaxation)
    Calcium ions actively transported into sarcoplasmic reticulum
  13. Three (relaxation)
    ATP breaks linkages btw actin and myosin filaments without breakdown of ATP itself
  14. Four (relaxation)
    breakdown of ATP "cocks" cross-bridges
  15. Five (relaxation)
    troponin and tropomyosin molecules inhibit he interaction btw myosin and actin filaments
  16. Six (relaxation)
    muscle fiber remains relaxed, ready to be stimulated