Intro to glial cells - focus on astrocytes

Question 1

Name the six types of glial cells mentioned in your lecture.

Answer 1

1) Oligodendrocytes
2) Schwann Cells
3) Radial glia
4) Astrocytes
5) Microglia
6) Ependymal cells

Question 2

Which of the glial cell types mentioned in your lecture do not come from the same precursor cells as neurons? Which lineage do they come from instead?

Answer 2

Microglia. They come from a macrophage lineage.

Question 3

What is the function of oligodendrocytes?

Answer 3

Responsible for myelin sheath in CNS.

Question 4

What is the function of schwann cells?

Answer 4

Responsible for myelin sheath in PNS.

Question 5

What is the function of ependymal cells?

Answer 5

Line the outside of the brain and the ventricles within the brain.

Question 6

What is the function of radial glia?

Answer 6

Direct neurons to their correct place during development.

Question 7

What is the function of microglia?

Answer 7

Immune cells of the brain. They detect damage.

Question 8

What are the functions of astrocytes? (List 6).

Answer 8

• support for CNS
• help form the blood brain barrier
• secrete neurotrophic factors
• maintain ionic homeostasis (by taking up K+, neurotransmitters, water)
• provide substrates for ATP production
• play a part in functional hyperemia

Question 9

Empty spaces in the brain are frequent; astrocytes are few and far between. True or false?

Answer 9

False. Empty spaces in the brain are incredibly infrequent. Astrocytes almost entirely surround neurons (are only absent in the actual synapse) and comprise roughly 50% of all brain cells.

Question 10

Astrocytes have their own territory, with very minor overlap between themselves and other astrocytes. True or false?

Answer 10

True.

Question 11

Which part of an astrocyte can make contact with local blood vessels?

Answer 11

The siphon process.

Question 12

Which feature underlies activity dependent changes in blood flow to the brain?

Answer 12

The link between astrocytes and blood vessels.

Question 13

List the 3 mechanisms by which astrocytes remove excess K+ from a synapse after an action potential.

Answer 13

1) Ion channels (increase in ECF K+ conc. drives movement of K+ into the cell).
2) Energy dependent transporters (e.g. Na+ K+ ATPase: Na+ out, K+ in).
3) Cotransporters (in response to Cl- and Na+, K+ moves against its conc. gradient into the cell).

Question 14

Astrocytes are connected to one another via ___ _________.

Answer 14

gap junctions.

Question 15

Gap junctions are permeable to small molecules. True or false?

Answer 15

True

Question 16

How do astrocytes get rid of an excess of a particular ion once they have removed it from a synapse? What is this process dependent upon?

Answer 16

They pass ions to other astrocytes via gap junctions. This process is concentration dependent. i.e. an ion flows from an area of high concentration to an area of low concentration.

Question 17

Is the direction of ion flow through gap junctions selective?

Answer 17

Only in terms of size.

Question 18

One gap junction is comprised of two ________.

Answer 18

connexons.

Question 19

Connexons themselves are comprised of 6 _________.

Answer 19

connexins.

Question 20

How are connexons (hemichannels) arranged to form a complete channel?

Answer 20

One connexon is embedded in the pre-synaptic membrane and one connexon is embedded in the post-synaptic membrane. A channel is formed by the pores in each membrane, extending through both hemichannels.

Question 21

Various molecules, ions and electrical impulses directly pass through a regulated gate between astrocytes. True or false?

Answer 21

True.

Question 22

Can connexons open and close?

Answer 22

Yes.

Question 23

Each connexin is a _ transmembrane spanning domain protein.

Answer 23

4

Question 24

Do astrocytes respond to glutamate?

Answer 24

Yes.

Question 25

Synaptic activity results in extravasation of K+. True or false?

Answer 25

True.

Question 26

Neuronal activity induces considerable changes in ECF pH (increase). List 3 mechanisms by which astrocytes help to lower the ECF pH back to normal.

Answer 26

• Na+/H+ exchanger
• Na+/HCO3- cotransporter
• Cl-/HCO3- exchanger

HCO3 = bicarbonate ion.

Question 27

Astrocytes respond to neurotransmitters because they express g-protein coupled receptors. True or false?

Answer 27

True.

Question 28

Astrocytes release gliotransmitters into the extracellular space via gap junctions. True or false?

Answer 28

False.

Question 29

Astrocytes respond to specific inputs via neurotransmitter receptors. Activation of neighbouring astrocytes occurs in two ways. List them.

Answer 29

• gap junction communication (spatial buffering)

- gliotransmitters (e.g. ATP)

Question 30

How do astrocytes respond to physical stimulation?

Answer 30

Activation of intracellular Ca2+ via IP3. IP3 and Ca2+ can both flow through gap junctions to affect other astrocytes. IP3 can activate intracellular Ca2+ in another astrocyte and Ca2+ can cause Ca2+ dependent Ca2+ release in another astrocyte. Whether both act together or alone, ultimately PLC activation is required for propagation to continue.

Question 31

Animals with more complex brains have more astrocytes per neuron. If astrocytes only played a supporting role, then this wouldn’t be the case. True or False?

Answer 31

True.

Question 32

In response to stimulation glia release neuractive

substances. What are these substances called?

Answer 32

Gliotransmitters.

Question 33

Astrocytes have all of the machinery to be able to put transporters into vesicles, to dock those vesicles at the membrane, and to release them in response to a signal. We used to think that this was exclusively in the realm of neurons.

They have the molecule synaptobrevin, syntaxin, SNAP-23; they have vesicular transporters, vesicles and they can acidify those vesicles.

Answer 33

True.