glial cells Flashcards
what cell types are found in the brain
macro and microglia and neurons
what cells are macroglia
astrocytes and oligodendrocytes and schwann
what does myelin compose? which matter
white matter in the brain
what is myelin
specialized membrane that surrounds axons and facilitates conduction through the axon in a rapid fashion
how does myelin speed transmission
it acts as an insulator along the axon allowing transmembrane currents at specific locations called nodes of ranvier
saltatory conduction
channels that allow ion flow and depolarization are only found in nodes of ranvier, in between myelinated sections of the axons and thus allows signal to skip down the length as action potentials are initiated and propagated.
how can we visualize myelin
MBP staining, luxol blue staining and Electron micrograph
benefits of myelin
reduces energy consumption needed to restore the proper ionic gradients. important for long term axonal health and maintenance
when does myelination occur
one of the last processes to occur in development. humans third trimester until the 2 year.
what fibers are the first to be myelinated?
motor fibers.
which are the last to be myelinated
association cortex.
which cells myelinate the PNS
schwann cells; any axon that is not in the brain or spinal cord.
which cells or the CNS
oligodendrocytes
where do schwann cells come from
neural crest cells
what other cells types are produced by neural crest
cartilage, bone, fibroblasts, doral root ganglia, melanocytes, smooth muscle and neurons
which gene can be used to detect schwann cell precursors
cad19
can schwann cells be cultured and detected?
yes. immature schwann cells can be identified by krox 20 they can be isolated from peripheral nerves
how many axons does one schwann cell associate with?
ONE; this one cells forms myelin around one segment of the nerve
which two proteins can be used to detect myelin?
MBP and MAG
what do schwann cells do after injury
the dedifferentiate, proliferate and produces agents that stimulate nerve repair
how do they differentiate and myelinate?
unknown mechanism, but it requires axon contact and probably involves signals from the axon.
Neuregulin 1
proteins that regulate cell fate. I and II are most abundant and they are expressed in neurons. both oligo and schwann produce receptors (NRG, ErbB 1/2/3
regulates thickness of myelination
what are oligodendrocytes
they are the macroglia that myelinate the CNS.
how many axons can one oligo myelinate
40-50
origin of oligodendrocytes
derived from early neural progenitors in the ventricular zone
how many waves of OL migration are there?
3
OPC wave 1
preoptic area
OPC wave 2
medial and lateral ganglionic eminences
OPC wave 3
cortex ventricular zone
where do oligos come from?
neural progenitor cells. but we dont know which one. NG2 positive cells or glial restricted progenitors
what problems from glial cell fate mapping studies
overlapping markers, cell culture conditions, KO’s are embryonic lethal, contradictory information
how do we identify oligo precursors
A2B5 and PDGFR. they are simple and bipolar
what can speed up OL differentiation
laminin (ECM) and Fyn kinase
what is Fyn kinase necessary for?
process extension
what is Fyn kinase
src family kinase (tyrosine), only member upregulated in OL development. gets recruited to cell membrane in response to signals. reguates process extension.
schwann cell summary
1) myelinate 1 axon segment because whole cell is in contact with axon
2) PNS myelin. conposition is different from CNS.
3) hard to observe differentiation in culture, unless co-culture
4) can promote neuronal repair after injury
oligodendrocytes summary
1) myelinate many axonss\
2) CNS is different than PNS
3) can easily assay in culture.
4) inhibits neural regeneration after injury.
what is myelination for
rapid nerve conduction
what is the most abundant glial cell
astrocytes
how much of total brain are astrocytes by volume
50%. 40-50% glial cell population
old theory of astrocytes
homogeneous population of non-excitatble cells that fill space between neurons
new reality of astrocytes
dynamic heterogeneous population of cell
astrocyte-to-neuron rule and ratio
there is an increase in the number of astrocytes per neuron with increasing brain complexity and size (4-7:1)
where are protoplasmic astrocytes found
gray matter
what do protoplasmic astrocytes do?
enfold neuronal cell bodies and prcesses they form multiple contacts with neurons (as many as 1 million) form end-feet with blood vessels
what do protoplasmic astrocytes look like?
stellate or star shaped with many fine complex processes.
what do fibrous astrocytes look like
stellate or star like with extensive processes scattered in the white matter of spinal cord and the brain
where are fibrous astros found
in the white matter
characteristics of fibrous
not as complex as protoplasmic, but have longer processes. run between myelinated fibers and contact axons at the nodes of ranvier. frequently form end-feet with capillaries
radial glia are what
specialized glial cells with long unbranched processes.
muller cells of retina
elongated throughout the thickness of the retina radial glial cell
bergmann glia
goli epithelial cells of the cerebellum that extend through the molecular layer to the cerebral cortex.
tanycytes
radial glial cells that located in the ependymal lining of the ventricles.
what do radial cells do
they are scaffolding for neuronal cell migration they are produced in early in development and provide substrate for migrating neurons.
what are astrocyte functions in neurogenesis and early development
1) scaffold for migrating neurons
2) help create brain microarchitecture
3) synaptogenesis
4) formation of the BBB
astrocyte functions in neuronal homeostasis
1) regulates extracellular K+
2) neurotransmitter uptake and inactivation
3) control local blood flow
4) provide metabolic support to neurons
5) pH regulation
6) energy regulation
astrocytes role in neuronal activity and plasticity
1) can regulate and limit number of synapses.
2) can aid in the maturation and stabilization of synapses
what proteins do astrocytes provide for ECM
tenascin C/R and brevican
glial Ephrin A and Neuron EphA4 interactions regulate dendritic spine morphology
BBB composition
composed of tight-junctino brain capillary endothelial cells that precludes entrance of substances into the brain.
seperates plasma from brain interstitial fluid.
what forms the proper barrior for the BBB
endothelial cells. the interaction with astrocytes is required for the development.
what ways do brain endothelial cells differ from regular
1) continuous tight junctions are present between the cells that prevents paracellular movement of molecules.
2) no detectable transednothelial pathways suhc as intracellular vesicles.
what factors induce the BBB in endothelial cells
TGF-B, Glial-derived growth factor, bFGF, angiopoetin1, interleukin-6
what factor is important for neurogenesis
neurogenin
what pathway is important for the neuro-glia switch
STAT3
what are microglia
resident macrophages of the brain.
what percent of the brain do microglia compose
15%. they are widely distributed throughout the brain.
what do microglia do
they are responsible for removing debris, and recrutied for injury. also pruning
where do microglia come from
they come from the yolk sac.
what is the fastest moving cell in the brain
microglia
what do microglia do during development
eliminate unused connections and control the stem cell populations/
what happens to microglia when they are activated
they assume an ameboid shape and migrate to areas of disease. they begin to produce immune molecules.
what factors and characteristics of good microglia
decreased inflammation and increased phagocytosis.
IL-6, IL-1B, TNF-a, TGF-B, CX3CR1, CD45, NO
what factors and characteristics of bad microglia
increased inflammation and decreased phagocytosis. CD40L, CX3CR1, CDK5/p25, s100B.
