Peripheral Nerve Injury

Question 1

Spinal cord anatomy

Answer 1

There is an anterior and posterior aspect of spinal cord
With anterior horns (motor) and posterior horns (sensory)

ANTERIOR HORNS- ventral root
POSTERIOR HORNS- dorsal root

they join to create spinal nerve which is a mix of both motor and sensory nerves

Question 2

Epineurium

Answer 2

Connective tissue that surrounds the spinal nerve

Question 3

Fascicle

Answer 3

Bundle of multiple nerves within the spinal nerve
There are multiple fascicles situated within the spinal nerve
Blood vessels are in and around the fascicles within the nerve

Perineurium surrounds the fascicle

There are more fascicles within the fascicles inside the nerve

Question 4

Perineurium

Answer 4

Surrounds the fascicles within the nerve

Important layer as this is usually what needs to be reattached when repairing a nerve

Question 5

Neuron inside a fascicle

Answer 5

Endoneurium surrounds the neuron

Inside the neuron there is a motor and sensory function

So any injury to a neuron can lead to motor or sensory dysfunction

Question 6

Causes of nerve damage

Answer 6

Cutting the nerve (surgery, penetrating injury)

Compression of nerve

Fracture (open of closed), causing nerve to be stretched, can also happen via dislocation

Crushing the nerve (trauma accident like motor vehicle crash)

Question 7

3 types of nerve injury

Answer 7

Neuropraxia
Axonotmesis
Neurotmesis

Question 8

Neuropraxia

Answer 8

• Mild demyelination of the neuron
  – endoneurium and axon not damaged
• Mild conduction block can be caused
• Complete spontaneous recovery every time after a few days or weeks
• loss of some types of sensation and power
• spontaneous recovery after a few days or weeks

EXAMPLES:
- crutch palsy
- Saturday night palsy

Question 9

Axonotmesis

Answer 9

• Damage to axon
• moderate demyelination
• Endoneurium undamaged
• moderate conduction block caused
• loss of conduction, but nerves are still intact

Recovery:
- Axonal regeneration starts within hours of nerve damage via neurotrophic factors
- usually gan complete refection and its usually spontaneous
- will take more time
- regeneration of nerve completed by WALLERIAN DEGENERATION AND REGENERATION

Example:
- open or closed fracture (usually closed)
- dislocation

Question 10

Neurotmesis

Answer 10

• Endoneurium is damage
• Axon is damaged
• Demyelination occurs
• Severe condition block will occur

Recovery:
- Wallerian degeneration and regeneration does occur but prognosis is poor
- Surgery may be needed
- resultant scarring may cause neuroma

Examples:
- open fractures
- gunshot wound (penetrating injury)

Question 11

Wallerian degeneration and regeneration

Answer 11

Process of repairing a damaged nerve

Split into 2 parts:
- Wallerian degeneration
- Wallerian regeneration

Question 12

Wallerian degeneration

Answer 12

made up of 2 parts:
- proximal segmental change
- distal segmental change

Proximal segmental change
- changes in the proximal segment (before the nerve injury)

the nucleus picks up signs of nerve injury:
- nucleus will start migrating to the periphery of cell body
- Nissl bodies will disperse themselves around the nucleus
- cell body will swell

2 parts to Proximal segmental change:
1) chromatolysis:
– DNA in nucleus, will change into MRNA
- The MRNA will move into nissl bodies (RER), where proteins will be made
– Proteins go into Golgi, packaged into vesicles which can then move down the axon towards the nerve injury

2) Degeneration of myelin and Schwan cell to the adjacent node of ranvier:
– Break down of Schwan cell towards the adjacent node of ranvier to create a proximal stump

Distal Segmental Change:
- changes in distal segment (after the nerve injury)

• start triggering a breakdown of the plasma membrane and myelin.
• will leave schwan cells sitting around axon
• endoneurium starts releasing chemicals:
  – 5 hydroxytryptamine (serotonin)
  – histamines

these molecules attract macrophages:
- the macrophages eat all fragments left over of axon and myelin

left with a proximal and distal stump

Question 13

Wallerian regeneration

Answer 13

1) Axonal sprouts occur (usually occur 24 hours after the injury) they connect to the distal stump

2) The Schwan cells cling to the axonal sprouts

3) Axon regenerated and myelin is regenerated

Question 14

Why are the Schwan cells so important in Wallerian regeneration

Answer 14

As they make sure the axonal sprouts are close together and connect to the distal stump

Question 15

Why cant neurotmesis heal with Wallerian degeneration and regeneration

Answer 15

Due to the endometrium being damaged
– it releases chemicals which attract macrophages
– stops axonal sprouts sprouting outwards

Question 16

Transient Ischemia

Answer 16

Happens when there is a temporary disruption in the blood supply to part of the brain

Symptoms:
- acute nerve compression
- 15 mins numbness and tingling
- 30 mins loss of pain sensibility
- 45 mins of muscle weakness
- Relief of compression results in recovery –> no nerve damage

Question 17

Double crush injury

Answer 17

Proposed by Upton and McComa 1973

Proposed that if a nerve is impaired at 1 location it makes that patient more susceptible to other entrapments along the same neuroaxis.