Musculoskeletal Growth and Repair: Nerves Flashcards
What are the components of an efferent motor unit?
- Anterior horn cell (gray matter of the spinal cord)
- Motor axon
- Muscle fibres (NMJ)
Where do the cell bodies of sensory units lie?
In posterior root ganglia (outwith the spinal cord)
Name the features of spinal nerves
- Anterior and posterior roots combine to form a spinal nerve
- They exit the vertebral column via an intervertebral foramen
Name the features of a peripheral nerve
- Distal to the nerve roots
- Bundles of nerve fibres
- Surrounded by Schwann cells
- Larger fibres are surrounded by myelin sheath
- Multiple layers of connective tissues surrounding axons
How are peripheral nerves structured?
Axons are coated with endoneurium and grouped into fascicles which are covered in perineurium and then grouped into nerves (covered in epineurium)
Name the common compression injuries
- Entrapment
- Carpal tunnel syndrome
- Sciatica (spinal root compressed by intervertebral nerve)
- Morton’s neuroma (digital nerve in 2nd or 3rd web space of forefoot)
What are the features of neurapraxia?
- Nerve is stretched or bruised
- Reversible conduction block (local ischaemia and demyelination)
- Good prognosis (weeks or months)
What are the features of axonotmesis?
- Endometrium intact but disruption of axons
- Severely stretched, crushed or directly hit
- Wallerian degeneration follows
- Recovery: sensory is often better than motor but not normal
Can peripheral nerves regenerate?
Yes
What are the features of neurotmesis?
- Complete nerve division
- Laceration or avulsion
- No recovery unless repaired
- Endoneural tubes disrupted (high chance of miswiring in regeneration
- Poor prognosis
What are the features of closed nerve injuries?
- Nerve injuries in continuity (neuropraxis and axontmesis)
- Spontaneous recovery is possible
- Surgery indicated after 3 months
- Examples: brachial plexus injuries and radial nerve injury caused by humeral fracture
What are the features of open nerve injuries?
- Related to nerve division (neurotmentic injuries)
- E.g. knives/glass
- Treated with early surgery
- Distal portion of the nerve undergoes Wallerian degeneration
What are the clinical features of nerve injuries?
- Sensory: anaesthesia, hypo/hyperaesthetic and paraesthetic (pins and needles)
- Motor: paresis (weakness), paralysis , muscle wasting and dry skin
- Reflexes: diminished or absent
Describe the healing of nerve injuries
- Initial death of axons distal to the site of injury
- Wallerian degeneration followed by degredation of the myelin sheath
- Proximanl axonal budding after roughly 4 days
- Regeneration at rate of roughly 1mm/day (higher in children)
- Pain is first modality to return
Which factors can predict the prognosis of nerve injuries?
- Pure or mixed nerves
- How distal the lesion is (proximal is worse)
