peripheral nerve injury

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peripheral nerve injury
2011-04-17 23:53:59
peripheral nerve injury

peripheral nerve injury
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  1. LMNL
    flaccid paralysis if a complete lession, muscle is denervated if complete lesion, hyporeflexia or areflexia
  2. UMNL
    can have flaccid paralysis, but spasticity is common, hyperreflexia
  3. spasticity
    inc resistance to a passive movement; hyperexcitability of the stretch reflex
  4. spasm
    • forceful involuntary muscle contraction response to injury, a protective isometric contraction of muscles
    • to splint or guard an injured area
  5. structure of a peripheral nerve
    • contains nerve fibers, connective tissue, blood vessels
    • contain both myelinated and unmyelinated axons
  6. each nerve fiber is surrounded by
    each group of fibers is surounded by
    each fasicle is surrounded by
    • endoneurium
    • perineurium
    • epineurium
  7. schwann cells
    • maintains myelination
    • 1:1 relationship
    • also found around unmyelinated axons
    • not 1:1 relationship
  8. axonal transport
    • antegrade- cell body to nerve terminal
    • retrograde- nerve terminal/ axon to cell body
  9. without the cell body
    • axons can't produce what they need
    • any part distal to the loss of the connection degenerates
    • degenerated sections can not propagate action potentials
  10. predictable manner of degeneration
    Wallerian degeneration
  11. neuropraxia
    • injury with only minor damage, nerve axons and connective tissue remain intact
    • no wallerian degeneration
  12. neuropraxia is characterized by
    • localized conduction block or slowing of action potentials througth the lesion
    • 1. focal demylination
    • 2. partial conduction block
    • 3. complete conduction block
    • minor compression injury which involves sensory and sympathetic involvement before motor
    • complete recovery immediately after decompression
  13. axonotmesis
    axon injury and continuity interrupted but intact epineurium (connective tissue tubes) are intact
  14. axonal interuption
    • wallerian degeneration distally
    • complete loss of function distal to site of lesion
    • connective tissue and schwann cell basement membrane remain intact
    • regeneration of axon occurs along intact neural tube 1-4 mm a day
    • mechanism of injury is traction or compression
  15. neurotmesis
    • complete interruption of nerve axon and all supporting connective tissue structures
    • wallerian degeneration distally
    • complete loss of function distal to site of lesion
  16. neurotmesis is characterized by
    • loss of distal neural tube as the nerve regenerates there is no well defined path to follow
    • sprouting at the proximal stump and regeneration is incomplete and usually poorly organized; recovery is rare
    • mechanism of injury includes severe traction, compression injury, or laceration
  17. morphological and physiological changes of denervated nerves
    • muscle atrophy
    • eventual replacement of muscle by fibrous and adipose tissue, total degeneration takes about 3 years in humans
  18. changes in muscle excitability
    • oscillations in resting membrane potentials
    • fibrillation
  19. if nerve regenerates and muscle fibers recieve innervation
    • enlarged motor units (greater # of muscles fibers innervated by the same axon)
    • histologic grouping of fiber types