Degeneration and regeneration Flashcards
What are the 4 neurone types
Bipolar
Unipolar
Multipolar
Pyrimidal cells
What type of muscles can nerves supply
Skeletal
Smooth
Cardiac
Secretory glands
What are Seddons three classification
- neuropaxia
- axonomotomesis
- neurotomesis
What is neuropoxia
Disturbance at myelination
What is axonotomesis
Injury at the level of the myelin sheath but the 3 layers are still intact
What is neurotomesis
When the entire nerve is completely damaged (connective tissue and axon)
What are the three connective tissue layers on a neurone
- endoneurium
- perineurium
- epineurium
What happens after axonotmesis
Wallerian degeneration
What is the most severe nerve damage according to Seddons classification
Neurotomesis
Is it possible to get recovery in neurotomesis
Not if the injury is really close to the cell body of the nerve
If a neurone is damaged in a neuronal chain what will happen
- The neurone that is innervating a damaged neurone will withdrawal
- the neurone after the damaged neurone will die as it is not being innervated
When a neurone is damaged how does the environment change
- myelin forming cells: oligodendrocytes and Schwann cells
- microglia: immune cells
- astroycytes
Where are oligodentroytes found
In the CNS
Where are Schwann cells found
In the PNS
What are oligodendrocytes
Myelinate more than one axon
What are Schwann cells
Myelinate only one axon
What is the role of microglia cells
Phagocytose damaged material
What happens minutes after a nerve injury
- synaptic transmission cut off
- Two ends of the axon will leak into intracellular fluid
- Cut ends will swell apart
What happens hours after a nerve injury
- synaptic terminal degenerates
- astroglia surround the synaptic terminal
What happens days to weeks after a nerve injury
- cell body undergoes chromatolysis
- distal stump of axon undergoes wallerian degeneration
What happens at chromatolysis
The cell body increases in metabolic activity and produces lots of proteins
Nucleus becomes displaced to the periphery margins
What happens at wallerian degeneration
The axon is digested by phagocytes
Tissue that is preserved forms hallow tubules
What happens to the axons at wallerian degeneration
Axon sprout into Schwann cells
What happens when a type S motoneruone supplies as type FF muscle fibre
The FF muscle fibre changes to a type S muscle fibre to match the nerve supplying it
What is the fate of a denervated and not reinnervated muscle in the acute phase
- muscle is paralysed
- muscle becomes areflexic (cannot get reflexes)
- muscle start to fasciculate
What is the fate of a enervated muscle in the chronic phase
- fasciculations subside to give enervation atrophy and disuse atrophy
- muscle dies
- muscle tissue is replaced by connective tissue
