lecture 3 astrocytes Flashcards by cam o

astrocyes are most abundant macroglia constitute____of total brain volume

20-50%

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3 identifiable types of astrocytes

1) Protoplasmic: (sheet-like; gray matter)
2) Fibrous: (stellate; white matter)
3) Radial: (thin unbranched; white matter)

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Protoplasmic located where and have what morphology

Gray matter astrocytes that
enfold cell bodies and processes
sheet-like; gray matter)

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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

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Radial located where and have what morphology

(thin unbranched; white matter)

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radial glia that are located in retnia

Müller Cells- elongated throughout the thickness of the retina

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radial glia that are located in cerebellum

Bergmann glia-Golgi epithelial cells –extend through the molecular layer to the cerebral cortex

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radial glia that are located in ependymal lining of ventricles (where cerebral spinal fluid is made)

Tanycytes: radial glia

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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

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one way astrocytes help with neuron migration

Scaffolding, The neuron moves by release and reformation of the adhesion beneath the cell soma CONTACT DEPENDENT

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what does Astrotactin 1 and 2

Neuron-glial adhesion molecules that mediates neuronal migration on glial fibers

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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

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_____ are the major motile structures involved in axon guidance and are located at the neurite tips.

Growth cones (GCs)

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Chemoattraction and Chemorepulsion in astrocytes is

a souluble factor

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Netrin is an example of a

Chemoattractant

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the landmark study by Banker, 1980

showed that you can culture neurons with astrocytes and astroccyte conditions media promotes neuron survial

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souluble factors released by astrocytes can

sustain growth and survival.

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astrocytes release ____ that are specific for subtypes of neurons

survial factors (ex BDNF, NGF)

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Axodendritic synapse

synapse on to dendrite

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axosomatic synapse

synapse on to cell body inhibitory inter neurons

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axoaxonic synapse

synapse on synapse

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quantal contentis

the number of effective vesicles released in response to a nerve impulse

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Astrocytes control the # of _______formed and

Participate in Synaptic Stability and ______

synapses,Maintenance

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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