L12 - Degeneration and regeneration of nerves and muscles after trauma

Question 1

What are the different permutations that neurones can express their actions?

Answer 1

1. Neurones supply skeletal muscles
2. Neurones supply smooth muscles
3. Neurones supply other neurones

Question 2

What is Seddon’s classification of nerve injuries?

Answer 2

1. Neuropraxia
2. Axonotomesis
3. Neurotmesis

Question 3

What is neuropraxia?

Answer 3

• Neurone loses ability to function normally (due to disturbance of myelination)
• Blunt neural injury due to external blows
• Nerve stretched or compressed beyond normal range
• Damage to surrounding myelin, not nerve
• Spontaneous recovery possible

Question 4

What is axonotomesis?

Answer 4

• Axons and myelin sheath damaged
• Result of stretch of a nerve or its severe crush
• Endoneurium, perineurium and epineurium remain intact
• Full recovery possible but will take months/ years

Question 5

What is neurotmesis?

Answer 5

• Nerve is divided
• Complete transection
• Spontaneous recovery does not occur
• Surgical repair possible but complete recovery not possible
• Sooner surgery is better

Question 6

What would be that fate of the pre-, post- and inter-neurone if the middle of the chain is severely damaged?

Answer 6

Pre = No effect??? 
Inter =  Die as a result of injury
Post = Die

Question 7

What are the different types of neuroglial cells found in the PNS?

Answer 7

1. Schwann cells

2. Satellite cells

Question 8

What are the different types of neuroglial cells found in the CNS?

Answer 8

1. Ependymal cells
2. Astrocytes
3. Microglia
4. Oligodendrocytes

Question 9

What would be the reaction to an injury within a damaged neurone minutes after injury is sustained?

Answer 9

• Neurone will immediately stop conducting AP beyond the site of injury
• The two ends of the cut axon will be exposed and they will start leaking intracellular fluid
• -> Axonal transport occurs in both directions
• The cut ends will soon pull apart, sealing themselves and swelling at the same time

Question 10

What would be the reaction to an injury within a damaged neurone hours after injury is sustained?

Answer 10

• Synaptic terminal degenerates - accumulating of neurofilaments, vesicles
• Astroglia surround terminal normally
• They react by causing terminals to be pulled away from postsynaptic cell

Question 11

What would be the reaction to an injury within a damaged neurone days/ weeks after axotomy after injury is sustained?

Answer 11

Fate of the proximal segment:
- The cell body will undergo chromatolysis
Fate of the distal segment:
- The distal stump of axon will undergo Wallerian Degeneration

Question 12

What is Wallerian degeneration?

Answer 12

• An active process of degeneration

????

Question 13

What is crush syndrome

Answer 13

• A severe (often fatal) condition that follows a severe crushing injury, particularly involving large muscle masses
• Characterised by fluid and blood loss, shock, haematuria, and renal failure
• Compression syndrome

Question 14

What is the general pathophysiology of crushing syndrome?

Answer 14

Crushing injury –> Ischaemic damage to muscles –> Release of toxic metabolites