Nerve Degeneration and Regeneration in the PNS

Question 1

What is the difference between anterograde and retrograde transport?

Answer 1

Anterograde is away from the cell body, retrograde is towards the cell body
Involves microtubules, motor proteins called kinesins

Question 2

State the sequence of events that occurs after trauma to a nerve

Answer 2

• nerve conduction stops
• cut ends lose some cytoplasm
• fusion of cut ends, swell due to anterograde transport
• synaptic bouton degenerates, uncontrolled release of NT, causes fasciculations and fibrillations
• schwann cells become phagocytic and recruit macrophages (Wallarian degeneration)
• nucleus become eccentric, nissl substance increases
• rapid protien synthesis
• proximal segment degenerates (clean start)
• schwann cells align longitudinally in endoneurial sheath
• axons sprout to bridge gap, many enter but only one persists

Question 3

What three things does regeneration require?

Answer 3

• neurotrophic factors
• growth associated proteins
• endoneurial sheath

Question 4

Explain what is meant by ‘fate of muscle depends on re-innervation’

Answer 4

a type II muscle fibre will change to a type I muscle if it is reinnervated by a small motor neurone rather than a large motor neurone

Question 5

PNS likelihood of repair is dependent on three things

Answer 5

age (younger is better)
location (close to NMJ is better)
type of injury (transient, crush or cut)

Question 6

What are the consequences of nerve trauma in the sequence that they can occur?

Answer 6

fasciculation/fibrillation
fibrillation and paralysis
atrophy and decreased bone density

Question 7

What are the three types of nerve trauma?

Answer 7

neuropraxia - transient block e.g. pins and needles
axonotmesis - axon damaged, endoneurium intact
neurotmesis - complte section, requires surgery

Question 8

What are the three causes of damage to the PNS?

Answer 8

ischaemia
trauma
disease e.g. MND, myasthenia gravis

Question 9

What are the spinal levels of the following reflexes?

1. ankle
2. knee
3. biceps
4. triceps

Answer 9

1. S1 S2
2. L3 L4
3. C5 C6
4. C7 C8

Question 10

Which roots are affected by a prolapsed IVD?

Answer 10

roots below and maybe at the same level

Question 11

Give examples of 2 mechanism for an upper brachial plexus injury.
Which rootlets are most likely to be affected?
What is the name of the resulting palsy?
How does the patient present?

Answer 11

increase angle between neck and shoulder e.g. pulled head during parturition, fall from height
C5, C6
Erb’s palsy
waiters tip position, arm hangs by side, is medially rotated, cannot be raised. loss of sensation of lateral arm

Question 12

Give examples of 2 mechanism for a lower brachial plexus injury.
Which rootlets are most likely to be affected?
What is the name of the resulting palsy?
How does the patient present?

Answer 12

excessive upward pull of limb e.g. during partition, hanging off a tree
C8, T1
Klumpke’s palsy
Loss of sensation over medial/posterior forearm, forearm is supinated, wrist and fingers are flexed, claw hand
May get horners syndrome (ptosis and miosis) if T1 is involved, sympathetic neurones in T1 damaged