Nerve regeneration Flashcards
Describe the process of Wallerian degeneration and list the typical histological features that accompany it (3)
Degeneration of severed axons after injury. Proximal: chromatolysis, swelling of cell body. Distal: degradation/phagocytosis of disconnected axon and associated myelin sheath by macrophages and Schwann cells
Outline the role of Schwann cells in the regeneration of peripheral nerves (4)
Remove debris, provide growth promoting substrate and guidance for regenerating axon, promote neuron survival by secreting neurotrophic factors, re-myelinate
Describe the role of the three (3) major types of glia/supporting cells in the failure of axon regeneration in the CNS (6)
Oligodendrocytes: release/upregulation of neurite growth inhibitory proteins; astrocytes: glial scar formation & upregulation of axon growth inhibitory proteoglycans; microglia: may further damage & kill stressed neurons
Outline the role of Schwann cells in the regeneration of peripheral nerves (3) [x3]
Remove debris, provide growth promoting substrate and guidance for regenerating axon, promote neuron survival by secreting neurotrophic factors, re-myelinate
Describe the role of the three (3) major types of glia/supporting cells in the failure of axon regeneration in the CNS (4½)
Oligodendrocytes: Release/upregulation of neurite growth inhibitory proteins
Astrocytes: Glial scar formation and upregulation of axon growth inhibitory proteoglycans
Microglia: May further damage and kill stressed neurons
Describe the process of Wallerian degeneration & list the typical histological features that accompany it (3)
Degeneration of severed axons after injury. Proximal: chromatolysis, swelling of cell body. Distal: degradation/phagocytosis of disconnected axon and associated myelin sheath by macrophages and Schwann cells
State the cause of Wallerian degeneration and outline its typical microscopic features (3)
When nerves/axons are severed; chromatolysis, swelling of neuronal cell body, degradation of disconnected axon and associated myelin sheath
Describe the process of Wallerian degeneration (2)
Chromatolysis, swelling of cell body, degradation of disconnected axon and associated myelin sheath
When a lesion in the nervous system occurs & nerve connections are disrupted, the injured neurons show certain distinct histological features. List these features (2)
Chromatolysis, swelling of cell body, degradation of axon and myelin sheath
Name the process (1)
Wallerian degeneration
Describe the process of Wallerian degeneration (2)
Chromatolysis, swelling of cell body, degradation of disconnected axon and associated myelin sheath
State the cause of Wallerian degeneration and outline its typical microscopic features (3)
When nerves/axons are severed; chromatolysis, swelling of neuronal cell body, degradation of disconnected axon and associated myelin sheath
Describe the influence of glial cells on neurons attempting to regenerate axons after CNS injury (4) [x2]
Overall, they prevent axon regeneration. Oligodendrocytes: express neurite-growth inhibitory proteins, e.g. Nogo; astrocytes: turn reactive, form glial scar and express axon-growth inhibitory proteoglycans; microglia: remove debris but promote inflammatory reaction and may release cytotoxic factors damaging neurons
Outline the role of the following cell types after an injury to the nervous system:
Schwann cells (2)
Phagocytosis of debris, expression of axon growth-promoting cell adhesion molecules, support of neuron survival and axon re-growth by neurotrophin secretion
Oligodendrocytes (2)
Inhibition of axon regeneration through up-regulation of several growth inhibitory proteins
Astrocytes (2)
Hypertrophy and formation of glial scar: mechanical barrier to axon re-growth, as well as up-regulation of inhibitory proteoglycans
Microglia (2)
Phagocytosis of cell debris, degradation of extracellular matrix, but also promotion of inflammation and cytotoxic effects on neurones
Contrast the recovery of a patient where the axon tracts in the spinal cord are completely severed, as opposed to a similar injury to a peripheral nerve.
In each case, is it likely that the lost functions can be restored? Justify your answer (10) (in your answer you should be able to List the different types of supportive cells in the PNS & CNS and outline the role that each plays after axonal injury)
Spinal cord: There is no recovery with a transaction of the spinal cord as CNS axons do not regenerate because astrocytes and oligodendrocytes express several proteins that inhibit axon regeneration after CNS injury, astrocytes form a glial scar that is an obstacle for regenerating axons, microglial cells clear away cell debris but may also kill injured neurones.
Peripheral nerve: there is a good chance of recovery of function because in the PNS, Schwann cells dedifferentiate and release neurotrophic factors that promote neurone survival. They also express cell adhesion molecules that promote axon regrowth. Eventually, they re-myelinate the regenerated axon.
