peripheral nerve injuries Flashcards
motor unit (efferent)
anterior horn cell (in grey matter spinal cord)
motor axon
muscle fibres (NMJ)
sensory unit
cell bodies in posterior root ganglia (outside spinal cord)
nerve fibres join to form..
anterior (ventral) motor roots
posterior (dorsal) sensory roots
spinal nerves
anterior and posterior roots combine to form a spinal nerve
exit vertebral column via intervertebral foramen
start of peripheral nerve
axons: what are they and what they covered with
long processes of neurons
coated with endoneurium
fascicles: what are they and what they covered with
groups of axons: nerve bundles
covered with perineurium
nerve: what are they and what they covered with
groups of fasicles
covered with epineurium
what do schwann cells do
surround neurones
A-alpha fibres
14 microns
60-100m/s
large motor axons
muscle stretch and tension sensory axons
A-beta fibres
12-14microns
30-60m/s
touch, pressure, vibration and joint position sensory axnos
A-delta fibres
6-8microns
10-15m/s
sharp pain, light touch and temp sensation
B fibres
2-5microns
3-10m/s
sympathetic preganglionic motor axons
C fibres
<1micron
<1.5m/s
dull, aching, burning pain and temp sensaton
types of trauma no peripheral nerve
direct: blow, laceration
indirect: avulsion, traction
different types of nerve injuries
neurapraxia
axonotmesis
neurotmesis
classical conditions of nerve compression
carpal tunnel: median nerve at wrist
sciatica: spinal root ocmpressed IV disc
morton’s neuroma: digital nerve 2nd/3rd web space forefoot
neurapraxia injury
nerve in continuity
stretched, bruised or compression
reversible conduction block: localised ischaemia and demyelination, area of nerve
prognosis good
axonotmesis
endoneurium in tact (tube in continuity) but disruption of axons
stretched ++++, crushed or direct blow
what follows axonotmesis
wallergian degerneration
distal to site of injury, nerve fibre dissapears but endoneurium tube remails. Nerve shrinks back
axonotmesis prognosis
prognosis fair
sensory recovery often bettrer than motor (often not normal but enough to recognise pain, hot + cold, sharp + blunt_
neurotmesis
complete nerve division
laceration or avulsion
repairing neurotmesis
no recovery unless repaired - direct suturing or grafting
endoneural tubes disrupted to high change of mis-wiring during degeneration - sensory nerves going down motor pathways etc.
closed nerve injuries
nerve injuries in continuity - neuropraxis, axontmesis
spontaneous recovery possible, surgery indicated after 3motnths
examples closed nerve injuries
brachial plexus injuries - falling onto shoulder
radial nerve - humeral fractures
open nerve injuries
assoc with nerve division - neurotmesis
treated w early surgery
nerve injuries clinical features: sensory
dysathesiae (disordered sensation)
anasethesis (numb), hypo+hyper-aesthetic, paraesthetic
nerve injuries clinical features: motor
parasis (weakness), or paralysis, wasting
dry skin: loss of tactile adherence since sudomotor fibres not stimulating sweat glands in skin
nerve injuries clinical features: reflexes
diminished or absent
healing of nerve injuries
slow
starts with initial death of axons distal to site of injury - Wallerian degeneration, then degredation of myelin sheath
proximal axonal budding after ~4days
regeneration process rate 1mm/day
pain first modality to reurn
prognosis for recovery depends on
whether nerve is pure (only sensory/motor) or mixed
how distal lesion is (proximal worse)
direct repair of nerve
laceration with ends close together
no loss nerve tissue
nerve grafting
nerve loss
late repair
UMN lesion vs LMN lesion: strength
U: decreased
L: decreased
UMN lesion vs LMN lesion: tone
U: increased
L: decreased
UMN lesion vs LMN lesion: reflexes
U: increased
L: decreased
UMN lesion vs LMN lesion: ankle clonus
U: present
L: absent
UMN lesion vs LMN lesion: Babinski’s sign
U: present
L: absent
UMN lesion vs LMN lesion: atrophy
U: absent
L: present
