What are the unique features of the CNS?
- selective vulnerability of neuronal systems: degeneration of specific nuclei and connections
- mature neurons are post mitotic
- anatomic/physiologic characteristics:
- bone enclosure
- metabolic substrate requirements
- no lymphatics
- limited immune surveillance (physical barrier)
- distinctive response to injury/healing: gliosis
What do neurons look like?
- large nuclei with prominent nucleolus
- well definted cytoplasm w/ Nissl substance (RER)
- shape varies depending on locatio in brain
- neuromelanin: contains dopamine, seen in substantia nigra, degenerates in Parkinsons
lipofucin - accumulates with aging
What are the 3 reactions of neurons to injury?
- Eosinophilic changes (ischemia/hypoxia)
- Central chromatolysis (axonal damage)
- Intraneuronal inclusion formation
Why does eosinophilic degeneration occur? When does it manifest at the light microscope? What is the morphologic criteria?
- Lethal ischemia, hypoxia, or hypoglycemia
- Takes 12024 hrs to manifest
- Shrinkage of neuronal cell body
- Loss of Nissl w/ cytoplasmic eosinophilia
- Loss of nucleolus w/ nuclear pyknosis
- Red is dead
- Eosinophilic degeneration
What occurs in central chromatolysis?
- manifestation of switch from manufacture of synaptic to structural proteins in response to axonal damage
- reversible if axonal repair is successful
- cellular swelling with margination of Nissl substance and nucleus and accumulation of filaments and organelles
- Central chromatolysis
- ballooned cell- loses concavity - nissl gets pushed to edge of membrane