Lecture 2: Peripheral Nerves Flashcards
What is neuritis?
Inflammation of a nerve.
What is interstitial neuritis?
Neuritis that affects the nerve’s stroma.
What is parenchymatous neuritis?
Neuritis that affects the nerve’s axons.
What are common causes of neuritis?
Infection, toxins (including alcohol, drugs, poisons, solvents), direct trauma, prolonged/severe compression, traction, extreme heat or cold, electrical stimulation, radiotherapy, some chemotherapy drugs, and conditions like diabetes that increase susceptibility.
What are the signs and symptoms of neuritis?
Very painful; pain experienced in tissues supplied by the nerve and in the nerve itself; pain is deep, lancinating, intensely achy, burning, constant but worsens with positions/movements stressing the nerve; local pressure/extremes of temperature cause extreme pain; motor weakness, spasms, fasciculations, irritable/depressed reflexes, hypaesthesia, hyperesthesia, paraesthesia, allodynia.
What can be observed in superficial neuritis?
A localized red streak on the skin corresponding to the inflamed nerve.
What is the RMT role during acute neuritis?
On-site direct techniques are contraindicated; avoid exacerbating inflammation/pain with positioning, manual techniques, and inappropriate hydrotherapy; address inflammation and pain using circumferential cold/cryotherapy (“donut compress”); refer to MD.
What are complications of neuritis?
Adhesions, compensatory problems, and permanent nerve damage, especially if prolonged.
What conditions are required for successful nerve regeneration?
- Healthy and intact cell body
- Adequate blood supply
- Adequate Schwann cell supply
- Absence of infection
- Intact endoneurial sheath (plus perineurium and epineurium)
- Close approximation of injured nerve ends
What are the nerve repair timeframes?
• Gap repair: 10–12 days post-injury
• Stabilized to minimal stress: 2–3 weeks post-injury
• Transmission detectable distal to injury: 4–6 weeks
What is the regeneration frontier?
The leading tip of new axons with reconstructed neurolemma and myelin sheath during regeneration.
How fast do new axons grow after gap repair?
1–2 mm/day (about 1 inch/month).
Why is the regeneration frontier highly excitable?
Because the axonal membrane is immature with a lower depolarization threshold, leading to irritable firing.
What is Tinel’s sign?
Percussion over a regenerating nerve causing tingling/pins and needles at the regeneration frontier or distally, used to locate the frontier.
What is a motor unit?
One alpha motor neuron together with the muscle cells it stimulates.
What symptoms occur when motor axons are injured?
Flaccid paralysis (atonia) or flaccid paresis (hypotonia), depending on extent.
What is flaccid paralysis of a motor unit?
Loss of firing due to motor neuron injury and Wallerian degeneration, leading to atonia.
What is flaccid paralysis of a muscle?
Paralysis of the entire muscle when all motor axons are injured.
What happens if all muscles for an action are paralyzed?
The action itself will be paralyzed (flaccid paralysis).
What is flaccid paresis?
Partial loss of firing due to some motor units being injured and others remaining intact, causing muscle weakness.
Can an individual motor unit be paretic?
No, motor units are either ON (normal) or OFF (paralyzed).
What causes motor irritable firing?
Partial nerve injuries where some motor axons are intact and others have degenerated, leading to spasms and fasciculations.
What are the reflex responses in motor nerve injury?
• Areflexia: Loss of reflex
• Hyporeflexia: Diminished reflex
• Hyperreflexia: Irritable firing (exaggerated reflexes/spasms/fasciculations)
What is true (denervation) atrophy?
Muscle wasting due to loss of alpha motor neuron innervation, leading to profound dystrophic changes.
Is true atrophy reversible?
Yes, if alpha innervation is restored before fatty degeneration (within 1–2 years).
What sensory zones are affected by nerve injuries?
• Area of isolated supply (sole): All sensory info travels via one nerve
• Primary zone: Most sensory info travels via one nerve, but some via others
What is anaesthesia in nerve injury?
Full loss of sensation due to complete severing of a peripheral nerve.
What is hypoaesthesia in nerve injury?
Diminished sensation due to partial nerve injury.
How can peripheral nerve injury affect proprioception?
Loss of proprioceptive signals from joints, muscles, and soft tissues.
What is the role of vasomotor function in the autonomic nervous system?
Sympathetic input signals smooth muscle in blood vessels to contract (vasoconstriction).
Which nerves carry the majority of limb autonomic fibers?
• Median nerve (upper extremity)
• Tibial/sciatic nerve (lower extremity)
What happens in vasomotor paralysis?
Complete autonomic denervation leads to full vasodilation, blood pooling, edema, vascular/tissue dystrophy, and gangrene risk.
What happens in vasomotor paresis?
Partial autonomic denervation causing irritable vasomotor firing: blanching, ischemic pain, goosebumps, sweating.
What clinical variables affect presentation of peripheral nerve injury?
- Responsibilities of the affected nerve (motor, sensory, proprioceptive, vasomotor)
- Injury location along nerve pathway
- Whether injury is complete or incomplete
- Presence of vasomotor dysfunction
- Presence of causalgia
- Neuroma formation
- Recovery status
What is causalgia?
Irritable firing from partially injured vasomotor-carrying nerves, causing burning pain, allodynia, hyperpathia, electric shock sensations, rubor/pallor, sweating/dryness, edema, pain, and skin atrophy.
What triggers causalgia?
Pressure, temperature changes, and emotional upset.
What is a neuroma?
A tangle of regenerating nerve fibers at the site of nerve transection, leading to a positive Tinel’s sign.
Why should friction be avoided over a neuroma?
To prevent aggravation and damage.
How can you tell if a nerve injury is recovering?
Presence of a regeneration frontier (positive Tinel’s sign moving distally).
What happens if a nerve injury becomes permanent?
No regeneration frontier develops; complete injury may become incomplete or stay complete.
In a recovering complete nerve injury, what will stimulation to the regeneration frontier cause?
SENSORY irritable firing only.
In a recovering complete nerve injury, where will SENSORY irritable firing be felt?
On-site and in distal supply tissues.
In a recovering complete nerve injury, what will stimulation to distal supply tissues cause?
NO irritable firing.
In a recovering incomplete nerve injury, what will stimulation to the regeneration frontier cause?
SENSORY and MOTOR irritable firing.
In a recovering incomplete nerve injury, where will SENSORY and MOTOR irritable firing be felt?
On-site and in distal supply tissues and muscles.
In a recovering incomplete nerve injury, what will stimulation to distal supply tissues cause?
SENSORY firing.
In a recovering incomplete nerve injury, where will SENSORY firing be felt when stimulating distal supply tissues?
On-site.
In a neuroma, what will stimulation on-site at the neuroma cause?
SENSORY irritable firing only.
In a neuroma, where will SENSORY irritable firing from on-site stimulation be felt?
On-site and in distal supply tissues.
In a neuroma, what will stimulation to distal supply tissues cause?
NO irritable firing.
What important note is associated with permanent nerve injuries regarding irritable firing?
Permanent nerve injuries may also be a source of irritable firing.
