Muscle Contraction

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Muscle Contraction
2013-04-19 11:49:39
BIO 220

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  1. What does muscle contraction do?
    reduces the length of each sarcomere
  2. Sliding filament model
    Mechanism of muscle contraction. Thin filaments ratchet across thick filaments to pull the Z lines together and shorten the sarcomere.  Myosin molecules on thick filaments attach to actin on the thin filament to form a crossbridge. It then bends inward, pulling the thin filament toward the center of the sarcomere, breaks the crossbridge, and forms a new crossbridge further down. 
  3. Energy for __ changes in __ comes from __.
    • conformational changes
    • myosin heads
    • hydrolysis of ATP (myosin head is an ATPase)
  4. Skeletal muscles contract when?
    when stimulated by lower motor neurons (via acetylcholine)
  5. What happens in a muscle at rest?
    myosin-binding sites on the actin are blocked by the regulatory protein strand (tropomyosin) in the thin filament.  Attached to tropomyosin is a troponin complex
  6. __ in the muscle cell plasma membrane (__) carry the resulting __ deep into the muscle cell.
    • Infoldings
    • transverse tubules
    • graded depolarization
  7. The __ membrane becomes __ and releases its __.
    • sarcoplasmic reticulum 
    • depolarized
    • store of Ca2+
  8. What do the calcium ions do?
    bind to troponin causing conformational (shape) change that moves tropomyosin and exposes the binding sites on actin; myosin heads attach and muscle contract. 
  9. The contraction is terminated as __.
    calcium is pumped out of the cytoplasm, back into the sarcoplasmic reticulum, by calcium pumps (calcium ATPase); as the calcium concentration falls, the tropomyosin-troponin complex again blocks the binding sites
  10. What does creatine phosphate do?
    indirectly provides most of the energy