What unique features does the central nervous system have that make it vulnerable to injury?
- Grouped by nuclei
- injury to one area can knock out all the relevant neurons
- Neurons are post-mitotic
- Enclosed in bone
- No lymphatics
What is the basic design of a neuron?
What shapes can be seen in different areas? (just an FYI)
Body with a large nucleus, Nissal substance, dendrites and an axon.
- Pyramidal neurons in cerebral cortex
- Purkinje cells in the cerebellum
- Globoid cells in the deep grey nucleus
- Many more
What is lipofuscin?
How does it appear on histology?
Oxidized unsaturated fatty acids that accumulate in neuron (and other tissue!) cytoplasm with age
It appears granular, yellow brown
Do you remember the six layers of the cerebral cortex?
How does this change in the visual cortex?
- Molecular Layer
- External Granular Layer
- External Pyramidal Layer
- Internal Granular Layer
- Internal Pyramidal Layer
- Multiforme Layer
- White Matter (not a part of the cortex)
In the visual cortex, layer four is exceptionally thick because of the high number of visual inputs and is divided into 4a, 4b, and 4c.
What layers are seen in the cerebellum?
From superficial to deep
- Molecular layer
- Purkinje cell layer
- Granular cell layer
- White matter
How do neurons react to injury?
What type of damage do each of these changes reflect?
Eosinophilic changes (reaction to ischemia/hypoxia)
Central chromatolysis (reaction to axonal damage)
Intraneuronal Inclusions (Discussed later, but multifactorial)
What changes can be seen histologically in neurons which have had lethal ischemic or hypoxic damage?
- Eosinophilic nuclei
- Shrunken cell body
- Loss of Nissal bodies
- Loss of nucleolus
- Condensation of chromatin
All of these changes are indicative of apoptosis/cell death.
Damage to the axon causes central chromatolysis. What causes these changes?
What changes are seen?
Are these changes permanent?
Damage to the axon prompts the cell to manufacture structural proteins to repair the neuron and not synaptic proteins.
Cellular swelling with Nissal bodies pushed to the side, production of organelles and filaments.
No, they can be reversed with time.
What are the "glial cells" of the CNS?
Where are they derived from?
Macroglia- Astrocytes, Oligodendrocytes, Ependymal cells
Microglia- resident macrophages
Macroglia are derived from neuroectoderm and microglia are derived from bone marrow.
What do astrocytes do in the CNS?
How are they typically visualized on histology?
- Contribute to the blood brain barrier
- Repair and form scars
- Maintain the extracellular environment
- Structural support
They are normally invisible unless there has been some damage, so they have to be visualized with antibodies against their main structural protein, GFAP.
What is reactive astrocytosis?
What is seen on histology?
Activation of astrocytes in response to pathologic processes
Astrocytes will divide and become larger or star-like.
What do oligodendrocytes do in the CNS?
What diseases have they been implicated in?
They create the myelination that surrounds neurons.
MS, progressive mulitfocal leukoencephalopathy, oligodendrogliomas
What are Ependymal cells?
What type of connections are seen between them?
Cuboidal ciliated cells that line ventricular surfaces
The lateral walls have cell junctions to form a CSF-brain barrier
What is choroid plexus?
What does it look like on histology?
Cells responsible for secreting CSF into the ventricles
papillary architecture with tight junctions extending into the ventricle
How do microglial cells appear on histology in normal tissue?
How do they appear on histology during infection?
slim, rod shaped nucleus and otherwise invisible.
May differentiate into foamy macrophages or condense into multi-nucleated giant cells.
What are meningothelial cells?
Groups of cells seen in the arachnoid membranes covering the brain and spinal cord