Peripheral Nerve Injuries Flashcards
Which cells form a thin cytoplasmic tube around peripheral nerves?
Schwann cells
What is the name of the membrane that coats the axon of the nerve?
Endoneurium
What is the name of the membrane that coats the fascicle of the nerve?
Perineurium
What is the name of the membrane that coats the nerve?
Epineurium
Nerve fascicles are bundles of what?
Axons
What does a bundle of fascicles form?
Nerve
What is the fiber category with the fastest conduction speed?
Aα
What is the thinnest fiber category?
C
Which nerve fiber category carries sharp pain, very light touch and temperature sensation?
Aδ
What type of sensations do category C nerve fibers carry?
Dull, aching, burning pain and temperature sensation
Which nerve fiber category carries touch, pressure, vibration and joint position sensory axons?
Aβ
What is neurapraxia?
Temporary loss of motor and sensory function due to blockage of nerve conduction, lasting six to eight weeks before full recovery - often from blunt trauma or shock injuries. Nerve remains intact.
What is axonotmesis?
Peripheral nerve injury in which the axons and their myelin sheath are damaged but the endoneurium, perineurium and epineurium remain intact. Usually the result of a more severe crush or contusion than neurapraxia, mainly follows a stretch injury.
What is neurotmesis?
Peripheral nerve injury in which both the nerve and nerve sheath are disrupted - partial recovery may occur but complete recovery is impossible.
What are three classical conditions of nerve compression?
Carpal tunnel syndrome (median nerve at wrist)
Sciatica (spinal root by intervertebral disc)
Morton’s neuroma (digital nerve in 2nd or 3rd web space of forefoot)
Can peripheral nerves regenerate?
Yes
In a closed peripheral nerve injury, when is surgery indicated?
If no recovery identified after 3 months
What are the symptoms of a nerve injury?
Dysaethesiae (disordered sensation)
- anaesthetic (numb), hypo- & hyper-aesthetic, paraesthetic (pins & needles)
Paresis (weakness) or paralysis +/- wasting
Dry skin
- loss of tactile adherence since sudomotor nerve fibres not stimulating sweat glands in skin
Reflexes diminished or absent
What is Wallerian degeneration?
Active process of degeneration that results when a nerve fiber is cut or crushed and the part of the axon distal to the injury (i.e. further from the neuron’s cell body) degenerates. (Primary culture studies suggest that a failure to deliver sufficient quantities of the essential axonal protein NMNAT2 is a key initiating event.)
At what rate does nerve regeneration proceed?
~ 1 mm/day
Which is the first modality to return in recovery from a nerve injury?
Pain
What is Tinel’s sign?
Distal tingling on percussion of the site of a damaged nerve
What is the ‘rule of three’ in surgical timing in a traumatic peripheral nerve injury?
Immediate surgery within 3 days for clean and sharp injuries
Early surgery within 3 weeks for blunt/contusion injuries
Delayed surgery, performed 3 months after injury, for closed injuries
What are the differences in clinical findings between upper motor neuron lesions and lower motor neuron lesions? (tone, deep tendon reflexes, clonus, Babinki’s sign, atrophy)
Tone - UMN increased LMN decreased Deep tendon reflexes - UMN increased LMN decreased Clonus - UMN present LMN absent Babinki's sign - UMN present LMN absent Atrophy - UMN absent LMN present
