Neuronal Injury

Question 1

most injuries to the nervous system affect the ____

Answer 1

axon

Question 2

what can affect nerves in the PNS or CNS?

Answer 2

physical trauma
vascular insufficiency (stroke)
metabolic disorders
tumours

Question 3

injury to the axon divides the neuron into ____ and ____

Answer 3

• proximal portion: retains attachment to cell body
• distal fragment

Question 4

what is a lesion?

Answer 4

impact on function

Question 5

chromatolytic reaction

Answer 5

proximal part of axon:
- eccentric nucleus (floats to one end)
- nissl substance fragmentation
- ^RNA and protein synthesis
- changes in expression of neuron’s genes

Question 6

wallerian degeneration

Answer 6

distal segment of injured axon:
- axonal degeneration
- myelin sheath fragmentation
- axonal & myelin debris is enveloped & destroyed by microglia

Question 7

transneuronal anterograde degeneration

Answer 7

postsynaptic neuron affected due to lack of input (NT) and eventually atrophies and dies depending on extent of neuronal damage

Question 8

transneuronal retrograde degeneration

synaptic stripping

Answer 8

neuron that provides injured cell with input:
synaptic space increases and is interrupted by glial processes (schwann cells in PNS; astrocytes/microglia in CNS)

Question 9

____ neurons have higher capacity to regenerate

Answer 9

peripheral neurons

Question 10

____ elements survive in the distal fragment of the axotomized neuron

Answer 10

connective tissue elements

Question 11

regeneration

the proximal fragment grows ____ that are guided to the distal portion by chemotropic factors secreted by _____

Answer 11

axonal sprouts; schwann cells

Question 12

regeneration process

Answer 12

• proximal fragment grows axonal sprouts guided to the distal portion by chemotropic factors secreted by schwann cells
• axonal growth is promoted and regenerated axons find their targets

Question 13

frey’s syndrome

Answer 13

regenerated axons guided to inappropriate targets

Question 14

what happens if axonal sprouts do not make contact with distal element?

Answer 14

axonal sprouts become entangled and form a benign mass (neuroma)

Question 15

factors contributing to decreased capacity of CNS neurons to regenerate

Answer 15

1. schwann cells
2. inhibiting factors
3. intrinsic differences
4. scarring & inflammation

Question 16

regeneration in PNS vs CNS

schwann cells

Answer 16

PNS:
- schwann cells produce growth promoting factors to promote axonal growth
- in embryo, both CNS & PNS nerves promote growty, only PNS retains ability

CNS: oligodendrocytes inhibit axonal growth in CNS

Question 17

regeneration in PNS vs CNS

inhibiting factors

Answer 17

• both PNS & CNS secrete growth promoting factors
• CNS also contains inhibiting factors
• central myelin = potent axonal growth inhibitor (CNS myelination occurs after growth is complete)

Question 18

regeneration in PNS vs CNS

intrinsic differences

Answer 18

CNS cells express proteins that render them less able to regenerate after initial formatting stages

Question 19

regeneration in PNS vs CNS

scarring & inflammation

Answer 19

in CNS injury:
- scar formation
- astrocyte proliferation
- microglia & other immune cell recruitment
- inflammation

if surrounding tissues are selectively excluded, healing is enhanced

Question 20

clinical considerations for regeneration

Answer 20

• introduction of trophic substances
• schwann cell grafts
• introduction of antibodies against axonal growth inhibitors
• transplantation of fetal tissue
• administration of immunosuppressants, anti-inflammatory steroidal agents