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2013-12-13 22:56:58

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  1. long duration MUAPs are seen when?
    early stages of deymelination 

    the discharge of APs is prolonged, so summation takes longer than usual.

    also seen in myopathy, but in that case there's also decreased amplitude
  2. long duration polyphasic MUs are seen when?
    describe what's going on
    indicates a neuropathy if > 10% of the MUs in a muscle are polyphasic

    • electrical conduction to each fiber in the MU is prolonged
    • some terminal end fibers of the axon lost their ability to conduct an AP and activate a muscle fiber
    • -->
    • lower number of muscle fibers contributing to the MUAP, so now the e characteristics of each stage are more distorted
    • --> multiple stages with prolonged duration

    appearance: multiple peaks, then a short group of squiggles
  3. large amplitude MUs - indicate what
    healing process after a chronic partial nerve injury 

    the high amplitude is a result of collateral sprouting that is now innervating extra muscle fibers
  4. myopathy
    disease affecting stability of muscle membrane

    leads to eventual muscle fiber necrosis

    Periph nerves are basically intact, so conduction of motor axons is WNL, tho in later stages may have changes in terminal branches of motor axons
  5. progression of myopathy results in
    • loss of viable muscle fibers
    • loss of strenght
    • changes in terminal branches of motor axons
  6. EMG changes in myopathy
    • short duration a/o low amplitude of MUAP
    • (can look like fibs, but start/stop under vol control)

    early complete interference pattern

    EMG is good to rule in/out myopathy
  7. short duration MUs happen why?
    loss of muscle fibers in MU

    The majority of the fibers contributing to overall duration of summated MUAP died off, so the MU looks electrically shorter in duration than normal.
  8. short duration MUs occur secondary to what?
  9. Low amplitude MU due to what?
    decrease in muscle fibers that contribute to peak summation MUAP
  10. neuropathic EMG
    long duration, long duration polyphasic, a/o large amplitude