L2: Intro to glia Flashcards
What are the two major classes of cells in the brain?
Neurons and Glia
Describe the electrical excitability of neurons and glia
- Neurons are electrically excitable,
- whereas glia are electrically non-excitable and cannot generate action potentials
Glia express voltage-gated channels, true or false?
True
Are glia vascular cells in the brain?
- No, glia are not vascular cells
What is the primary function of glia in the brain?
Glia are the homeostatic cells of the brain
Name the two types of glia
macroglia and microglia
What is the origin of macroglia, and name some examples
- Macroglia has a neural ectodermal origin
- Examples include astroglia, oligodendroglia, and NG2-glia
What is the origin of microglia, and how do they invade the brain?
- Microglia have a non-neural mesodermal origin
- They originate from macrophages that invade the brain during fetal development
Name some examples of peripheral (NS) glia
- Schwann cells
- satellite cells of sensory and sympathetic
- ganglia- olfactory ensheathing cells
- enteric glia
Describe the morphology of astrocytes
Astrocytes have a classical star-like morphology with two types: protoplasmic and fibrous
What intermediate filaments do astrocytes express?
Astrocytes express GFAP (Glial Fibrillary Acidic Protein) as intermediate filaments
Where can astrocytes form processes under the surface of the brain?
- Astrocytes can form processes under the surface of pia matter, forming the glial limitans
What do astrocytes enwrap around in the blood-brain barrier (BBB)?
- Astrocytes enwrap capillaries in the BBB
How many dendrites of a single neuron can a single astrocyte contact?
- A single astrocyte can contact multiple dendrites of a single neuron
Is there overlapping between astrocytes?
- Usually, there is no overlapping between astrocytes
How many neuronal axons does an oligodendrocyte myelinate, and how close is it to the cell body?
An oligodendrocyte myelinates 30-50 neuronal axons within 20-30 micrometers of the cell body (soma)
What is the function of NG2 glia?
NG2 glia form contacts, including synapses with neurons in grey matter, and can generate oligodendrocytes during developmental remodeling
What is the origin of microglia, and what is their role in the brain?
Microglia have a mesodermal origin and form the brain’s immune system. They appear in three states: resting, active, and phagocytic
What is the role of Schwann cells, and what are the two types?
- Schwann cells have the role of myelinating and non-myelinating peripheral nerves
-The two types are myelinating Schwann cells & non-myelinating Schwann cells
What are the two types of synapses that connect via transcellular channels?
The two types of synapses are chemical synapses and electrical synapses
The two types of synapses are chemical synapses and electrical synapses
- A tripartite synapse consists of three components: the presynaptic terminal, the postsynaptic membrane, and the surrounding astrocyte process
What triggers the release of neurotransmitters and glial transmitters in a synapse?
- Calcium triggers the release of neurotransmitters and glial transmitters in a synapse
How do glial cell receptors facilitate cell-to-cell communication?
- Glial cell receptors facilitate cell-to-cell communication through ionotropic and metabotropic receptors
What is volume transmission, and how does it occur?
- Volume transmission is a slow process that involves one-to-many transmissions via diffusion
What is wiring transmission, and how does it occur?
- Wiring transmission is a rapid process that occurs via chemical synapses or electrical synapses, involving a one-to-one transmission
Do astrocytes fire action potentials?
No, astrocytes do not fire action potentials.
How do astrocytes respond to neurotransmitters and blood hormones?
Astrocytes respond to neurotransmitters and blood hormones by using calcium ions for signalling
What happens when one astrocyte cell is activated by a neurotransmitter?
- When one astrocyte cell is activated by a neurotransmitter, the signal spreads across other astrocytes, leading to inter-glial calcium waves
How are inter-glial calcium waves maintained?
- 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
What are gliotransmitters, and what are some examples?
- signaling molecules released by astrocytes
- Examples include glutamate, ATP, and D-serine
- How do gliotransmitters modulate firing frequency and synaptic transmission?
- Gliotransmitters such as glutamate, ATP, and D-serine can bind to respective receptors on neurons to modulate firing frequency and synaptic transmission
Apart from gliotransmitters, what other substances do glial cells release?
Glial cells also release peptides such as NPY
What is the main function of astrocytes in the brain?
- support
- homeostasis (particularly K+ buffering)
- water regulation
- regulation of extracellular pH
- maintenance of the BBB properties & the astrocyte-neuronal lactate shuttle
How do astrocytes maintain K+ homeostasis in the brain?
- 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.
What role does astrocytes play in water regulation in the brain?
- 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
How do astrocytes contribute to the maintenance of the blood-brain barrier properties?
- Astrocytes contribute to the maintenance of the blood-brain barrier properties by interacting with endothelial cells & helping to regulate the permeability of the BBB
What is the astrocyte-neuronal lactate shuttle?
- 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
What is the main function of oligodendrocytes in the central nervous system (CNS)?
- to myelinate axons in the CNS, which helps in the rapid transmission of nerve impulses
How do microglia respond to trauma or damage in the brain?
- 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
