Nerves

Question 1

Nerve Response to Loading

Answer 1

"TARD"
Type
Amount
Rate
Duration

Question 2

Factors of Nerve Excursion

Answer 2

1. Elongation of nerve bed = adjacent segments move towards
2. Shortening of nerve bed = adjacent segments move away
3. Adjacent segments move first –> as movement continues more distal segments undergo excursion
4. Adjacent segments have the greatest magnitude of excursion

Question 3

Steps of Nerve Rupture

Answer 3

1. Nerve straightens
2. Fascicles straighten
3. Axons straighten + tension (remove undulations)
4. After 4% strain axons rupture
5. Some fascicles rupture
6. Critical number of fascicles rupture –> failure of entire nerve and plastic deformation

Question 4

Nerves Under Compression

Answer 4

1. uniform circumferential
   - displaces contents transversely and longitudinally
   - force greatest at edge of cuff due to the shearing forces
2. lateral (between 2 flat surfaces)
   - change in shape but not volume = no increase in endoneurial pressure
   - less damaging

Question 5

Axonal Crush/Transection

Answer 5

1. neuropraxia = temporary conduction block (schwann cell damage)
2. axonotmesis I = loss of axon continuity
3. axonotmesis II = loss of axon + endoneurium continuity
4. axonotmesis III = loss of axon + endoneurium + perineurium continuity
5. neurotmesis = complete transection of nerve trunk

Question 6

Axonal Transection Stimulates:

Answer 6

“Wearing My Dad’s Socks”

1. Macrophage infiltration (1-4 days)
2. Wallerian degeneration (2-4 days) = distal axonal degeneration + myelin fragmentation
3. Schwann cell differentiation = detach from axons, proliferate, recruit macrophages to clear cellular/myelin debris
4. Schwann cells Align longitudinally + express stimulating factors to direct nerve regrowth toward target organ

Question 7

Chronic Nerve Compression Injury

Answer 7

“Injury Gradually Saves Face”

1. Axonal integrity initially preserved (neuropraxia)
2. Gradual macrophage infiltration (several weeks)
3. Schwann cell turnover, proliferation + apoptosis (peaks at 4 weeks) triggered by Schwann cell mechanosensitivity
4. Focal demyelination (7-10 days) –> remyelination (2-4 weeks) –> new thinner myelin sheath –> decreased conduction velocity but normal NMJ

Question 8

Chronic Nerve Compression Causing Intraneural Oedema

Answer 8

1. ischaemic damage to endoneurial capillary endothelial cells
2. damage to blood-nerve barrier
3. increased intraneural pressure
4. impairs intraneural blood flow + axoplasmic flow
5. fibroblasts activated + fibrosis

Question 9

Nerve Pathology Risk Factors

Answer 9

Diabetes
Thyroid disease
Nerve disorder (predisposes for secondary nerve disorder = double crush phenomena)