Peripheral Nerve Degeneration Flashcards
Identify & define the indicated components of the provided image:
- Enodneurium: surrounds individual axons
- Perineurium: bundles groups of axons into fascicles
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Epineurium: surrounds groups of fascicles & also forms the protective sheath on the nerve
- find blood supply
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Which Sunderland degree classifications of nerve injury do not require physician intervention?
1, 2, & 3
What tests can be performed in order to classify the degree of nerve injury?
sensory & motor testing
nerve conduction studies
surgery
MRI - Diffusion Tensor Imaging
What defines the proximal end of a nerve injury? Distal end?
Proximal: where all the axons are still attached to the soma
Distal: only has axons (that will degrade)
What is the human response to nerve injury? How does it work?
Wallerian Degeneration (Controlled inflammatory response)
getting rid of distal end → clearing everything up, then regrow the axon to innervate the target tissue
- Degeneration (distal axon)
- Regeneration (of proximal axon)
- Re-innervation (target tissue)
Where in the body does Wallerian degeration occur? Why?
ONLY in PNS
degeneration in CNS is too slow (b/c oligodendrocytes do not help the same way the schwan cells do),
regeneration is not supported b/c it is not a permissive environment (d/t development of glial scars- that helps make sure structure is still intact, but inhibits growth)
Describe what happens within the first 24 hrs of Wallerian Degeneration
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Calcium influx from extracellular space (both in proximal & distal end) → induces a sealing of the ends
- proximal part usually degenerates up to first node of ranvier
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Degeneration
- proximal part usually degenerates up to first node of ranvier
- all of distal nerve degenerates
- Myelin breakdown begins
- resident macrophages begin clean up (induced by intact schwann cells)
Describe what happens by 48hrs of Wallerian Degeneration
- Axon & myelin breakdown continues distally
- myelin debris inhibits outgrowth from proximal stump
What variable is important in determining timeline of Wallerian Degeneration?
Where the injury occurred & the length of distal nerve that needs to be degenerated & how much needs to be regenerated
(ie. if injury in proximal arm, a lot of nerve needs to be degenerated, much less if injury is in finger)
What substance inhibits the outgrowth of the axon from the proximal stump?
myelin debris
Describe what happens by 72hrs of Wallerian Degeneration
- more macrophages called in from circulation that build up along whole distal nerve
- reactive Schwann cells proliferate & line up → begin to form tube : Bands of Bungner
What is the purpose of the Bands of Bungner?
the regrowing axon will use a guidance to find the target tissue
Describe what is happening about 1 week into Wallerian Degeneration?
- macrophages subside (when debris of myelin is mostly cleared up)
- substances are gone that inhibit the growth cone
- anti-inflammatory agents are present
- reactive Schwann cells continue to form Bands of Bungner → basically ready to be used as a cue for regrowth
Describe what is happening weeks-years into Wallerian Degeneration?
- once the regrown axon has found the target tissue (to increase conduction speed)
- Schwann cells are regenerating myeline
- axon fiber matures & thickens
- hopefully → regain of function
24-36 hrs post injury, Schwann cells release what substances? This has what effect?
- Proinflammatory agents → signal to resident macrophages to start clearing debris
- TNFa
- IL-1B