lecture 3 astrocytes Flashcards
astrocyes are most abundant macroglia constitute____of total brain volume
20-50%
3 identifiable types of astrocytes
1) Protoplasmic: (sheet-like; gray matter)
2) Fibrous: (stellate; white matter)
3) Radial: (thin unbranched; white matter)
Protoplasmic located where and have what morphology
Gray matter astrocytes that
enfold cell bodies and processes
sheet-like; gray matter)
Fibrous located where and have what morphology
stellate; white matter) scattered in of spinal cord and brain
• frequently form endfeet with capillaries
• run between myelinated fibers
Radial located where and have what morphology
(thin unbranched; white matter)
radial glia that are located in retnia
Müller Cells- elongated throughout the thickness of the retina
radial glia that are located in cerebellum
Bergmann glia-Golgi epithelial cells –extend through the molecular layer to the cerebral cortex
radial glia that are located in ependymal lining of ventricles (where cerebral spinal fluid is made)
Tanycytes: radial glia
lamellipodium
is a cytoskeletal protein actin projection on the leading edge of the cell. It contains a quasi-two-dimensional actin mesh; the whole structure propels the cell across a substrate
one way astrocytes help with neuron migration
Scaffolding, The neuron moves by release and reformation of the adhesion beneath the cell soma CONTACT DEPENDENT
what does Astrotactin 1 and 2
Neuron-glial adhesion molecules that mediates neuronal migration on glial fibers
how the function of Astrotactin 1 and 2 shown
- Antibodies to Astn1 can halt migration in vitro
2. Astrotactin null animals have delayed neuronal migration and behavioral defects
_____ are the major motile structures involved in axon guidance and are located at the neurite tips.
Growth cones (GCs)
Chemoattraction and Chemorepulsion in astrocytes is
a souluble factor
Netrin is an example of a
Chemoattractant
the landmark study by Banker, 1980
showed that you can culture neurons with astrocytes and astroccyte conditions media promotes neuron survial
souluble factors released by astrocytes can
sustain growth and survival.
astrocytes release ____ that are specific for subtypes of neurons
survial factors (ex BDNF, NGF)
Axodendritic synapse
synapse on to dendrite
axosomatic synapse
synapse on to cell body inhibitory inter neurons
axoaxonic synapse
synapse on synapse
quantal contentis
the number of effective vesicles released in response to a nerve impulse
Astrocytes control the # of _______formed and
Participate in Synaptic Stability and ______
synapses,Maintenance
Astrocyte -Neurogenesis scaflolding main pts
Directing neuron migration via direct cell contact
Directing neuron migration via chemo-attraction and repulsion
Astrocyte -Neurogenesis Survival main pts
Secretion of growth (survival) factors
Astrocyte -Neurogenesis main pts Synaptogenesis
Control the # of synapses formed
Maintain neuronal synapses
astrocytes Maintenance of Neuronal Homeostasis main ways (5) KNOW THIS
K+ homeostasis pH regulation Neurotransmitter homeostasis (uptake and inactivation) Redox balance and energy metoblism
in a resting membrane potential k+
K+ is higher intracellularly and lower extracellularly
during and action potential k+ is
K+ is lower intracellularly and higher extracellularly
astrocytes help maintain K+ homeostatis mainly by
Na+/K+ ATPase—uptake in astrocytes 5-fold higher than in neurons
astrocytes help maintain K+ homeostatis what is an channel assicated with this (important)
K+ channels (Kir4.1)
astrocytes remove K+ from the ECM by
buffering K+ when put back into the ECM by astrocytes
siphoning K+ to the blood
Kir4.1 expressed predominantly in brain
astrocytes and retinal Muller cell
Kir4.1 allow large ______ at potentials negative to EK
and small, but significant, outward K+ currents at those positive to EK
inward K+ currents
Why is maintaining extracellular K+ levels important?
Predispose the cell to hyper-excitability
Depolarization Block
(sizures
Important as many cellular processes are pH dependent including
enzymes, NMDA receptor and affects redox state of a cell.
Na+/H+ exchanger (1:1) : drives H+ out of cell by using energy of Na+ gradient
restores pHi normally and during acid loads
) Cl-/HCO3- exchanger (1HCO3- out:1 Cl- in) Na+ -independent.
Primarily extrudes HCO3- restoring pHi during alkaline loads.
Na+/Cl-/HCO3- (1Na+ in: 1HCO3- in: 1Cl- out): Na+ -dependent
Primarily drives HCO3- in during acid loads or following alkaline shifts extracellularly.
Na+:HCO3- co-transporter (1:3) dominant mechanism for the steady state maintenance and restoration of pHi and pHe
acid shift extracellularly then HCO3- is extruded; if alkaline shift them HCO3- is taken up.
in astrocytes PNT = Plasma Neurotransmitter Transporter function s
mainly to remove
neuron released glutamate.
Physiological Functions of NT Uptake(3)
1) Help terminate synaptic transmission
2) Protect synapse from inappropriate activation by excess
transmitter (e.g., glutamate)
3) Provide transmitter precursors to neurons
glutamate is an excitotoxin bcuz
is it builds up in EDM if over excites NMDA receptor
The HCO3/CO2 buffer system is extremely important because
it can be rapidly readjusted in alkalosis and acidosis
Oxidation is
the loss of electrons or an increase in oxidation state by a molecule, atom, or ion.
Reduction is
the gain of electrons or a decrease in oxidation state by a molecule, atom, or ion.
Glutathione (GSN) major thiol-disulfide redox ___ of cells
buffer
Glutathione (GSN) acts both
enzymatically and non-enzymatically.
although ______ has more GSN per cells there are more ______ in the brain
microglia, astrocytes
GSH helps with
redox reactions (helps remove radiacal O2 species), cell divison, antioxidant
Thus, brain glucose varies directly with changes in
blood levels.
is GSN increased or reduced in cultured neurons without neurons
reduced
Glucose gains access to brain and into cells by specific carriers
(glucose transporters) -
Astrocyte-Neuron ____Shuttle
Lactate
Lactate produced locally within brain Crosses the blood brain barrier If given in vitro (experimental preps)
lactate consumed preferentially over glucose!
EAAT- Excitatory Amino Acid Transporter (i.e., transports glutamate)- rely on Na+ gradient (does not require ATP for uptake but cell uses ATP to restore Na+ gradient). This type of pump is
s said to be electrogenic.
GFAP- Intermediate filament protein -used as a marker to
distinguish astrocytes from other glial cells.
Alexander’s Disease
Alexander’s Disease Caused my mutations in GFAP – glial fibrillary acid protein
