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LMNL
flaccid paralysis if a complete lession, muscle is denervated if complete lesion, hyporeflexia or areflexia
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UMNL
can have flaccid paralysis, but spasticity is common, hyperreflexia
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spasticity
inc resistance to a passive movement; hyperexcitability of the stretch reflex
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spasm
- forceful involuntary muscle contraction response to injury, a protective isometric contraction of muscles
- to splint or guard an injured area
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structure of a peripheral nerve
- contains nerve fibers, connective tissue, blood vessels
- contain both myelinated and unmyelinated axons
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each nerve fiber is surrounded by
each group of fibers is surounded by
each fasicle is surrounded by
- endoneurium
- perineurium
- epineurium
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schwann cells
- maintains myelination
- 1:1 relationship
- also found around unmyelinated axons
- not 1:1 relationship
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axonal transport
- antegrade- cell body to nerve terminal
- retrograde- nerve terminal/ axon to cell body
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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
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predictable manner of degeneration
Wallerian degeneration
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neuropraxia
- injury with only minor damage, nerve axons and connective tissue remain intact
- no wallerian degeneration
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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
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axonotmesis
axon injury and continuity interrupted but intact epineurium (connective tissue tubes) are intact
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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
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neurotmesis
- complete interruption of nerve axon and all supporting connective tissue structures
- wallerian degeneration distally
- complete loss of function distal to site of lesion
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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
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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
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changes in muscle excitability
- oscillations in resting membrane potentials
- fibrillation
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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
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