Degeneration and Regeneration of Peripheral Nerves Flashcards
Structural features of a nerve that can be affected by insult
Epineurium, perineurium, endoneurium, myelin sheath, axon
What is neuropraxis?
When a neurone temporarily loses its ability to function normally
What structural feature is affected by neuropraxis?
Myelin sheaths
What is axonotmesis?
Damage of axons along with their myelin sheaths
Restoration of function after axonotmesis
Endoneurium, perineurium and epineurium act as guidance tubes for new nerve sprouts to grow and re-supply target
What is neurotmesis?
When the entire nerve fibre is completely severed
What happens minutes after injury of a neurone?
- Neurone immediately stops conducting AP beyond site of injury
- Both cut ends start leaking intracellular fluid
- Cut ends pull apart, sealing and swelling
What happens an hour(ish) after injury of a neurone?
- Synaptic terminal degenerates
- Astroglia surround terminal
What happens days/weeks after injury of a neurone?
- Distal segment stump undergoes Wallerian degeneration
What happens to distal segment of severed nerve?
- Dies due to lack of nutrition
- Axon undergoes Wallerian degeneration and digested by phagocytes
- Other layers remain as hollow tubes to guide regrowth (of proximal end)
What happens to proximal segment of severed nerve?
- Undergoes chromatolysis
- Cell body makes proteins for repair
- Injured stump seals to form neuroma
- Stump regenerates to reinnervate
What happens to non-reinnervated muscle (acute + chronic phases)?
Acute phase:
- Flaccid paralysis
- Becomes areflexic
- Starts to fasciculate (twitch)
Chronic phase:
- Denervation atrophy (lose bulk due to denervation)
- Disuse atrophy (lose bulk due to no use)
- Muscle dies
- Muscle replaced by connective tissue (incl. fat)
