Glia

Question 1

general glia facts

Answer 1

majority of cells in the brain, have receptors for NT and can release NT

serve many functions including: supporting neurotransmission, maintaining ionic balance, trophic support

different from neurons: lack axons, retain ability to survive, do not generate action potentials

Question 2

types of glia

Answer 2

microglia

macroglia: oligodendrocytes, schwann cells, ependyml cells, astrocytes

Question 3

microglia overview

Answer 3

macrophages of the nervous system, serve as the immune cells of the brain.

origin: myeloid lineage. Yolk Sac. collinate in the brain early in development
role: surveilence (constantly sampling environment), phagocytosis, synaptic maintencence

Question 4

microglia response to tissue injury

Answer 4

Question 5

microglia sculpt synapses

Answer 5

during development or after injury

Question 6

Oligodendrocytes vs Schwann cells

Answer 6

Oligodendrocytes: Makemyelin, Found in CNS, Highly branching, Myelinate multiple axons/axon segments (up to 40 axons)

Schwann Cells: Make myelin, Found in PNS, One cell makes one myelin sheath

Question 7

myelin

Answer 7

made of lipids and proteins, extension of cells, each process of oligodenrocytes or a single schwann cell wraps around a small portion of an axon to myelinate it, region that is myelinated is called internode, two internodes are separated by myelin free region called node of ranvier, myelin increases conduction velocity of nerve impulses (saltatory conduction)

Question 8

disorders of myelin

Answer 8

multiple sclerosis: autoimmune attack on oligodendrocytes, loss of myelin loss of myelinated axons, unknown etiology, can be induced in rodents by injection of mylin resident proteins (MOG, PLP, MBP)

Question 9

ependymal cells

Answer 9

form lining of ventricles, involved in creating CSF, have cilia (important for movement of CSF through ventricles

Question 10

astrocytes

Answer 10

named for classic star shape, most common glial cell

Question 11

fibrous astrocytes

Answer 11

found in white matter, orient parallel to neuronal axons, higher levels of GFAP, big/long fibers, role in K+ homeostasis

Question 12

protoplasmic astrocyte

Answer 12

found in grey matter, very fine processes, little cytoplasm, very negative membrane potential (~-90 mV), prominent glutamate uptake, lower levels of GFAP

Question 13

non-overlapping spacial domains

Answer 13

astrocytes have a tiling effect, single astrocyte ensheaths an average of 4 neronal cell bodies (can contact up to 100k sypases in mice and 2m in humans)

Question 14

vasculature contact

Answer 14

astrocytes form perivascular end-feet around CNS capillaries and arteries

greater than 80% of capillary surface covered by astrocyte processes

helps form BBB

Question 15

synapse contact

Answer 15

astrocytes are an important component of synapses, NT release activates astrocytes, glial resonse to NT is increase in Ca2+ and release of transmitters (allow astrocytes to modulate neuronal activity)

Question 16

dynamic extension and retraction

Answer 16

astrocytes extend and retract their fine processes in response to stimuli

Question 17

astrocyte number and complexity

Answer 17

increase in number and complexity evolutionarily

Question 18

Answer 18

Question 19

radial glia during development

Answer 19

scaffold for migrating cells, structural support, source of progenitor cells

Question 20

synapse formation and maintenance

Answer 20

astrocytes regulate synapse formation (synaptogenesis), modulate synaptic strength (influence insertion of AMPA receptors into neurons), remove synapses (like microglia especially during early development)

Question 21

control of cerebral blood flow

Answer 21

neuron activity influences blood flow via astrocyte (vessels expand after contact with NT, which increases flow of RBC), known as neurovascular coupling or functional hyperemia, basis of BOLD signal during fMRI

Question 23

K+ spatial buffering

Answer 23

K+ goes out, hyperpolarization, need to remove K+ to facilitate further neuronal signaling -> astrocyte does passive K+- Cl- uptake, active transport via Na+K+ATPase,

AND K+ transfer by current flow through astrocyte syncytium via gap junctions called K+ spatial buffering

Question 24

NT clearance

Answer 24

no extracellular digestion of glutamate- cleared by glutamate transporters on astrocyte (EAAT1/GLAST and EAAT2/GLT1)

ensures crisp synaptic transmission, limits amplitude or duration of synaptic signaling, limit excitotoxicity (spill over of NT), operate in reverse direction when Na+ gradients depleted

EAAT2/GLT1: predominant transporter, incredibly abundant, enriched in astrocyte areas near synapses, decreases in expression causes disease

Question 26

NT recylcing

Answer 26

glutamate-glutamine cycle: glutamate cleared into astrocyte, glutamate converted to glutamine by glutamine sythetase (keeps intracellular glutamate concentration low), glutamine exported to neurons, converted back to glutamate by glutaminase, glutamate precursor for GABA - important for inhibitory cells

Question 27

metabolic support

Answer 27

astrocyte to neuron lactate shuttle hypothesis, glucase taken up at endfoot processes via glucose transporters, glucose converted to lactate, lactate exported to neurons, converted to pyruvate to enter TCA cycle

Question 28

reactive astrocytosis

Answer 28

sense and survey environment, following inflammation there is hypertrophy of processes, increase in Ca2+ signaling, upregulation of GFAP, loss of GS, gliosis (proliferation of astrocytes)

Question 29

epilepsy

Answer 29

bouts of hypersynchronous activity in the brain, decreased K+ buffering (causes more depolarization), decreased glutamate removal, decreased glutamate-glutamine cycling (decrease in GABA, shift toward excitation)

Question 30

Alexander’s disease

Answer 30

astrocytic disease, mutation in GFAP gene, leads to abnormal accumulation of GFAP into Rosenthal fibers

causes seizures, spasticity, developmental delays, hindbrain dysfunction