Injury and Repair of the Nervous System

Question 1

What happens to a nerve after damage in terms of secondary spread?

Answer 1

Anterograde (Wallerian) degeneration, retrograde degeneration (axonal die back), degeneration to the cell body is possible

Question 2

What does the success of nerve repair depend upon?

Answer 2

Severity of initial injury (what and how much has been damaged) and the extent of the secondary damage

Question 3

What are the three types of nerve damage?

Answer 3

Neurotmesis, axonotmesis and neurapraxia

Question 4

Describe neurotmesis (3rd degree nerve damage)

Answer 4

Both the axons and the nerve sheath are disrupted; the myelin, axons and epineurium are affected leading to Wallerian degeneration and largely this is irreversible damage

Question 5

Describe axonotmesis (2nd degree nerve damage)

Answer 5

Disruption of axons resulting from severe crush or contusion; the myelin and axon are affected and therefore there is Wallerian degeneration involved, but epineurium are still intact and is reversible

Question 6

Describe neurapraxia (1st degree nerve damage)

Answer 6

Results in temporary loss of motor and sensory function due to blockage of nerve conduction; myelin is affected but the rest of the neurone remains intact, and is reversible damage

Question 7

Describe Wallerian degeneration

Answer 7

Peripheral nerve is cut, distal part is disconnected from cell body and degenerates –> distal Schwann cells unwrap from the dead fragments –> divide to form continuous line of cells lining the distal endoneurial sheaths –> proximal cut ends of the nerve fibres form growth cones –> start to grow back down the sheaths guided by chemical factors (cell adhesion molecules) on the surface of Schwann cells –> macrophages engulf degenerated axon and myelin from distal stump –> Schwann cells proliferate and start to wrap myelin around regenerated fibres –> fibres are initially very thin and slow conducting

Question 8

Describe the process of nerve degeneration

Answer 8

Schwann cells divide and secrete trophic factors to attract the axon regrowth, and the Schwann cells then remyelinate the axon to facilitate repair

Question 9

Why is injury that affects the Schwann cell body of a neurone unlikely to regenerate?

Answer 9

Factors cannot be secreted which facilitate nerve repair, and therefore surgical intervention is required

Question 10

What can prolonged muscle enervation lead to?

Answer 10

Muscle atrophy and fibrosis, profound decrease in numbers of regenerating axons

Question 11

What is Tinel’s sign?

Answer 11

Lightly tapping over nerve to elicit a sensation of tingling in the distribution of the nerve

Question 12

What is the function of a glial scar formed in damage to the CNS?

Answer 12

Engulfs debris, seals lesion site, repairs BBB and expresses substances to inhibit axon growth

Question 13

What is involved in the treatment of a CNS injury?

Answer 13

Neuroprotection (contain the effects of early trauma), promotion of axonal regeneration (provide positive trophic support), guide axonal growth and rehabilitation therapy