2b: Neuronal plasticity and repair

Question 1

Repair has greater chance of success if…(3)

Answer 1

1.) Cell body is intact
2.) Crush injury involving axons (more distal = better chance) transection is the worst
3.) Basement membrane and CT coverings are intact.
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Question 2

1. ) What do fascicles contain? What are they bound by?

2. ) What are each axon bound by?

Answer 2

1.) Fascicles contain a bundle of axons (un-, lightly-, and heavily-myelinated axons). Bound by perineurium
2.) Each axon surrounded by endoneurium.
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Question 3

Describe neurotmesis, i.e. cause, result, recovery.

Three possible outcomes

Answer 3

-Usually results from severed nerve.
-Same reaction as axonotmesis (Wallerian degeneration, chromatolysis), but nerve less likely to reconnect with target.
1.) Successful target reconnection.
2.) Incorrect target reconnection.
3.) Connection with CT elements = NEUROMA = painful sensations.
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Question 4

What is the typical critical period and what happens after?

Answer 4

Typical critical period is during first 14 years of life, after which change becomes permanent (by-and-large). 
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Question 5

What are the two known populations of neural stem cells (where are they and what do they do)?

Answer 5

1.) Subgranular zone (dentate gyrus): Add neurons to hippocampus; related to learning.
2.) Subventricular zone (lateral ventricle): ???
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Question 6

Describe neuropraxia, i.e. cause, result, recovery.

Answer 6

-Result of a mild injury.
-Local demyelination, no degeneration. Temporary loss of conduction.
-Recovery expected; function restored when lesion removed.
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Question 7

What three factors (variables) allow a synapse to persist past the development stage?

Answer 7

1.) Presynaptic signal (neurotransmitter).
2.) Postsynaptic cell response (receptor).
3.) Retrograde signal from the postsynaptic element to the presynaptic element.
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Question 8

Give five characteristics of chromatolysis.

Answer 8

1.) Downregulation of everyday genes.
2.) Upregulation of growth-related genes.
3.) Nucleus displaced peripherally.
4.) Cell body swells (due to activating genes that repair the cell body distally).
5.) Ribosomes disperse.
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Question 9

Give the events after PNS damage (5; including damage)

Answer 9

1.) Transection of peripheral nerve axon.
2.) Wallerian degeneration (anterograde).
3.) Axonal segment and its myelin removed by Schwann cells and macrophages.
4.) Schwann cell proliferation (they also release trophic factors).
5.) Axonal sprouting (from the proximal end) at site of injury.
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Question 10

Give an example of synaptic strength adjustment during nervous system development in later life.

Answer 10

Presynaptic: May increase rate of NT release.
Postsynaptic: May increased NT receptor density.
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Question 11

Describe axonotmesis, i.e. cause, result, recovery.

Answer 11

-Usually result of a compression injury.
-Proximal axon, Schwann cells, and CT covering (endoneurium) remain (Wallerian, chromatolysis).
-Axonal sprouting —> Reconnection with target usually occurs because structural elements of nerve remain intact.
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Question 12

What happens to nervous system repair capabilities later in life?

Answer 12

Decrease in repair capabilities. 
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Question 13

1. ) What is the purpose of neurotrophic factors (2)?
2. ) Where to they come from?
3. ) How do they get into neurons?

Answer 13

1.) Survival of neurons during development, maintains metabolism of cell and processes. More important during development than in later life
2.) Target cells produce them. Different nerve cells and processes will depend on different trophic factors.
3.) Retrograde transport into soma; cells compete for neurotrophic factors.
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Question 14

Name three neurotrophic factors

Answer 14

1.) NGF
2.) BDNF
3.) Neurotrophins (NT-3, 4, 5)
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Question 15

Define the critical period, its timing, and its variability. When is it maximal?

Answer 15

Critical period: Period of maximal plasticity. Onset and duration is variable. Varies across different regions of the brain. Once over, brain responds differently to damage. 
-Infant has greater capacity for plasticity than an adult. 
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Question 16

What does plasticity mean in the nervous system context (2)? Example?

Answer 16

1.) Alterations in the pattern of apoptosis.
2.) Reorganization of synaptic connectivity.
e.g. If you lose two fingers, the cortex redistributes connections so that the now unused connections are used by the remaining digits (#30).
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