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21 Cards in this Set
- Front
- Back
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Glial cells involved in...
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Tumors, MS, neurodegeneration, physical/stab wounds
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Glia (general)
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Do not directly propagate AP
Retain ability to divide Neuroectoderm or mesoderm (microglia) CNS: astrocytes, oligodendrocytes, microglia, NG2 cells, Ependymal cells PNS: Satellite, Schwann |
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Astrocytes
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20-50% brain volume
Largest Single astrocyte can contact 100k synapses, also contact cell bodies, dendrites, axonal surfaces, blood vessels and capillaries Derived from radial glial cells, processes retract and become progenitors of adult astrocytes Bergmann (cerebellum) and Mueller (retina)-different Mitochondria (need ATP so are active) Distinguish by glial fibrillary acidic protein (GFAP) Heterogeneity amongst species |
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Two types of Astrocytes
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Protoplasmic: thick, highly branched processes, localized in gray matter associated with neurons
Fibrous: long, thin, less branched, in white matter with axons Regional heterogeneity exists (each are concentrated in different regions) |
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End Feet
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Wrap around blood vessel and capillaries and release vasoactive substances
Surround endothelial cells of BBB- perivascular lining membrane Glia limitans: thick layer of joined end feet at surface of brain, covered by outer basal lamina which makes contact with pia mater serve as passageways for transfer of nutrients from blood to neurons |
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Functions of Astrocytes
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Neuronal migration and guidance (radial glia cells provide scaffold)
produce and secrete growth factors for neurons (glial cell derived neurotrophic factor GDNF) Source of ECM proteins/adhesion molecules- support synaptic connections Physical barrier (protoplasmic, end feet/glial limitans) Reactive astrogliosis: astrocytes become activated with injury and fill void or wall off injury- glial scar Source of innate inflammatory mediators (microglia too-their communication is critical) Maintain brain homeostasis-control blood flow, remove NT and ions (glutamate) so buffer extracellular space (uses ammonia so decreases its levels), provide E and substrates for neurotransmission |
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Tripartite Synapse
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presyn and post sun neuron with astrocyte
communicate with neurons bidirectionally contact and chemical transmission Gliotransmitters: glutamate, D serine, ATP, TNF alpha |
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Astrocytes (pathogenesis)
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Glial scars
Amyotrophic lateral sclerosis (release toxic factors that kill motor neurons) Tuberous Sclerosis and Epilepsy- astrocytes in tubers and impairment of glutamate buffering Glioma- Astrocytomas most common glial tumor (glioblastoma multiform most deadly) |
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Oligodendrocytes
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Few branches
smaller than astrocytes In both gray (perineural oligodendrocytes) and white (myelination of axons- interfascicular oligodendrocytes) One oligo can construct and maintain several myelin sheaths, very tight sheet like processes of plasma mb, cytoplasm excluded (myelin is 80/20 lipid/protein) |
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Myelin
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sheath not continuous along axon
Myelinated segment called internode, then node of ranvier (lower resistance, rich in Na channels) |
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Oligodendrocytes (pathogenesis)
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Multiple sclerosis: idiopathic inflamm demyelinating disease, oligos and myelin degenerate
PML- caused by JC virus Clinical depression- loss of oligos and myelin oligodednrogliomas- slow growing, from perineural oligodendrocytes (so must have some kind of function, but today its unknown) |
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Microglia
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Smallest
20% of total brain glia Yolk-sac derived myeloid cells (monocyte/MO lineage) |
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Resting vs Activated Microglia
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Resting: small rod shaped soma, symmetrical processes- this conformation during health
Activated: graded response, aka reactive microglia; thicker processes and larger soma (non phagocytic), can form ameboid shape for movement (phagocytic) |
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Microglia Functions
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Resident immune cells of brain
QUICKLY activate to pathological changes Survey brain and phagocytose debris mediate CNS inflammatory response (chemokines, cytokines, TNF alpha) Phagocytose degenerating cells during CNS development |
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Quad-partite synapse
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Presynaptic, postsynaptic neurons, astrocyte and microglia
So microglia communicate both with neurons and astrocytes Involved with how synapse strength is maintained |
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Microglia (pathogenesis)
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Secondary Cell death- following stroke and trauma, TNF alpha and IL1 beta are neurotoxic and secreted from activated microglia
Bacterial meningitis; TNF and IL1 opens BBB and exacerbates bacterial infection HIV: microglia targeted Neurodegenerative: with increased microglia activation, parkinsons, alzheimers (try to chew up amyloid plaque in alzheimer's) MS, Autism, env toxicants Activated by Meth |
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NG2 Glia
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Most abundant progenitor cell in postnatal brain
Give rise to polydendrocytes which then form oligodendrocytes Maybe also give rise to astrocytes and neurons |
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Satellite Cells
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Surround cell bodies of sensory and autonomic ganglia
Regulate external environment, respond to ATP Connected by gap junctions Respond to Injury and produce proinflammatory molecules |
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Schwann Cells
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Derived from neural crest
Myelin around peripheral axons- similar to CNS except 1 schwann cell per 1 internode/axon, Small pockets of cytoplasm called schmidt lanterman clefts, BASAL LAMINA covers external surface of schwann cell Unmyelinated axons in PNS are enclosed in Schwann cell envaginations/canals |
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Schwann Cell Functions
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Myelination
phagocytose damaged axons Guide regeneration by forming tunnel toward target neuron produce neurotrophins Essential for maintenance of healthy axons |
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Schwann cells (pathogenesis)
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Guillain-Barre Syndrome- acute inflammatory demyelinating polyneuropathy, muscle paralysis, etiology unknown but half from acute infection, "autoimmune disease", lower limb/face weakness first with rapid ascending progression
Chronic inflammatory demyelinating polyneuropathy Charcot Marie Tooth disease: auto dominant demyelinating neuropathy, most common inherited neuro disorder, not fatal, foot drop, onset in adolescence, Many forms, CMT1A- duplication of peripheral myelin protein 22 leading to abnormal myelin sheath "onion bulb"- not as tightly wound Schwannomas- encapsulated and easily removed |
