L2: Intro to glia

Question 1

What are the two major classes of cells in the brain?

Answer 1

Neurons and Glia

Question 2

Describe the electrical excitability of neurons and glia

Answer 2

• Neurons are electrically excitable,
• whereas glia are electrically non-excitable and cannot generate action potentials

Question 3

Glia express voltage-gated channels, true or false?

Answer 3

True

Question 4

Are glia vascular cells in the brain?

Answer 4

• No, glia are not vascular cells

Question 5

What is the primary function of glia in the brain?

Answer 5

Glia are the homeostatic cells of the brain

Question 6

Name the two types of glia

Answer 6

macroglia and microglia

Question 7

What is the origin of macroglia, and name some examples

Answer 7

• Macroglia has a neural ectodermal origin
• Examples include astroglia, oligodendroglia, and NG2-glia

Question 8

What is the origin of microglia, and how do they invade the brain?

Answer 8

• Microglia have a non-neural mesodermal origin
• They originate from macrophages that invade the brain during fetal development

Question 9

Name some examples of peripheral (NS) glia

Answer 9

• Schwann cells
• satellite cells of sensory and sympathetic
• ganglia- olfactory ensheathing cells
• enteric glia

Question 10

Describe the morphology of astrocytes

Answer 10

Astrocytes have a classical star-like morphology with two types: protoplasmic and fibrous

Question 11

What intermediate filaments do astrocytes express?

Answer 11

Astrocytes express GFAP (Glial Fibrillary Acidic Protein) as intermediate filaments

Question 12

Where can astrocytes form processes under the surface of the brain?

Answer 12

• Astrocytes can form processes under the surface of pia matter, forming the glial limitans

Question 13

What do astrocytes enwrap around in the blood-brain barrier (BBB)?

Answer 13

• Astrocytes enwrap capillaries in the BBB

Question 14

How many dendrites of a single neuron can a single astrocyte contact?

Answer 14

• A single astrocyte can contact multiple dendrites of a single neuron

Question 15

Is there overlapping between astrocytes?

Answer 15

• Usually, there is no overlapping between astrocytes

Question 16

How many neuronal axons does an oligodendrocyte myelinate, and how close is it to the cell body?

Answer 16

An oligodendrocyte myelinates 30-50 neuronal axons within 20-30 micrometers of the cell body (soma)

Question 17

What is the function of NG2 glia?

Answer 17

NG2 glia form contacts, including synapses with neurons in grey matter, and can generate oligodendrocytes during developmental remodeling

Question 18

What is the origin of microglia, and what is their role in the brain?

Answer 18

Microglia have a mesodermal origin and form the brain’s immune system. They appear in three states: resting, active, and phagocytic

Question 19

What is the role of Schwann cells, and what are the two types?

Answer 19

• Schwann cells have the role of myelinating and non-myelinating peripheral nerves
  -The two types are myelinating Schwann cells & non-myelinating Schwann cells

Question 20

What are the two types of synapses that connect via transcellular channels?

Answer 20

The two types of synapses are chemical synapses and electrical synapses

Question 21

The two types of synapses are chemical synapses and electrical synapses

Answer 21

• A tripartite synapse consists of three components: the presynaptic terminal, the postsynaptic membrane, and the surrounding astrocyte process

Question 22

What triggers the release of neurotransmitters and glial transmitters in a synapse?

Answer 22

• Calcium triggers the release of neurotransmitters and glial transmitters in a synapse

Question 23

How do glial cell receptors facilitate cell-to-cell communication?

Answer 23

• Glial cell receptors facilitate cell-to-cell communication through ionotropic and metabotropic receptors

Question 24

What is volume transmission, and how does it occur?

Answer 24

• Volume transmission is a slow process that involves one-to-many transmissions via diffusion

Question 25

What is wiring transmission, and how does it occur?

Answer 25

- Wiring transmission is a rapid process that occurs via chemical synapses or electrical synapses, involving a one-to-one transmission

Question 26

Do astrocytes fire action potentials?

Answer 26

No, astrocytes do not fire action potentials.

Question 27

How do astrocytes respond to neurotransmitters and blood hormones?

Answer 27

Astrocytes respond to neurotransmitters and blood hormones by using calcium ions for signalling

Question 28

What happens when one astrocyte cell is activated by a neurotransmitter?

Answer 28

- When one astrocyte cell is activated by a neurotransmitter, the signal spreads across other astrocytes, leading to inter-glial calcium waves

Question 29

How are inter-glial calcium waves maintained?

Answer 29

- Inter-glial calcium waves are maintained by diffusion of a second messenger through gap junctions OR by calcium-dependent release of glial transmitters such as ATP and glutamate

Question 30

What are gliotransmitters, and what are some examples?

Answer 30

- signaling molecules released by astrocytes - Examples include glutamate, ATP, and D-serine

Question 31

- How do gliotransmitters modulate firing frequency and synaptic transmission?

Answer 31

- Gliotransmitters such as glutamate, ATP, and D-serine can bind to respective receptors on neurons to modulate firing frequency and synaptic transmission

Question 32

Apart from gliotransmitters, what other substances do glial cells release?

Answer 32

Glial cells also release peptides such as NPY

Question 33

What is the main function of astrocytes in the brain?

Answer 33

- support - homeostasis (particularly K+ buffering) - water regulation - regulation of extracellular pH - maintenance of the BBB properties & the astrocyte-neuronal lactate shuttle

Question 34

How do astrocytes maintain K+ homeostasis in the brain?

Answer 34

- Astrocytes maintain K+ homeostasis by taking up K+ from the extracellular space and transporting it into the perivascular system or interstitium - The process involves inwardly rectifying K+ channels and gap junctions that allow K+ movement between neighboring astrocytes.

Question 35

What role does astrocytes play in water regulation in the brain?

Answer 35

- Astrocytes regulate local shrinkage due to neurotransmitter release by accumulating water at places with high neuronal activity - Water is taken up by astrocytes through aquaporin 4 channels colocalized with K+ inwardly rectifying channels

Question 36

How do astrocytes contribute to the maintenance of the blood-brain barrier properties?

Answer 36

- Astrocytes contribute to the maintenance of the blood-brain barrier properties by interacting with endothelial cells & helping to regulate the permeability of the BBB

Question 37

What is the astrocyte-neuronal lactate shuttle?

Answer 37

- a process by which astrocytes take up glucose, convert it to lactate, and then release lactate to be taken up by neurons as an energy source

Question 38

What is the main function of oligodendrocytes in the central nervous system (CNS)?

Answer 38

- to myelinate axons in the CNS, which helps in the rapid transmission of nerve impulses

Question 39

How do microglia respond to trauma or damage in the brain?

Answer 39

- Microglia respond to trauma or damage in the brain by becoming activated: - with some aiming to destroy foreign cells - while others function as phagocytic cells to remove damaged cells and debris