L7: Glia - Form and Function

Question 1

What are the primary functions of astrocytes?

Answer 1

Astrocytes are involved in neural communication by enveloping synapses, maintaining ion homeostasis (e.g., potassium buffering), and uptaking neurotransmitters. They also provide metabolic support, transferring energy from blood vessels to neurons.

Question 2

What is myelination, and which cells are involved?

Answer 2

Myelination is the process of insulating axons to facilitate faster electrical signals. Schwann cells perform myelination in the peripheral nervous system, and oligodendrocytes do so in the central nervous system.

Question 3

How do Schwann cells differ from oligodendrocytes in function?

Answer 3

Schwann cells promote axon regeneration and wrap around a single axon in the peripheral nervous system, whereas oligodendrocytes wrap around multiple axons and inhibit regeneration in the central nervous system.

Question 4

What is the primary role of microglia?

Answer 4

Microglia act as the resident immune cells of the central nervous system. They detect and respond to pathogens, damage, and ATP release, transforming into phagocytic cells when needed.

Question 5

What is reactive astrogliosis?

Answer 5

Reactive astrogliosis is a process where astrocytes respond to brain injury by proliferating, changing shape, and forming glial scars that inhibit axon regrowth.

Question 6

Describe the structure and function of ependymal cells.

Answer 6

Ependymal cells line the walls of the brain ventricles and are involved in producing and circulating cerebrospinal fluid (CSF) via their cilia.

Question 7

Why were glial cells historically considered less interesting than neurons?

Answer 7

Glial cells do not generate action potentials, making them invisible to electrophysiological techniques, which led to a focus on neurons that exhibit electrical excitability.

Question 8

How do astrocytes support energy metabolism in neurons?

Answer 8

Astrocytes take up glucose from the blood, convert it to lactate, and supply it to neurons as an energy source, especially during high activity.

Question 9

What is the significance of gap junctions in astrocytes?

Answer 9

Gap junctions connect astrocytes, allowing them to form large syncytial networks for communication and coordinated responses across brain regions.

Question 10

What role do microglia play in neuroinflammation?

Answer 10

Microglia release pro-inflammatory molecules like cytokines in response to infection or damage, contributing to neuroinflammation, which can be both protective and pathological.

Question 11

What are the morphological differences between macroglia and microglia?

Answer 11

Macroglia (e.g., astrocytes, oligodendrocytes) are larger and involved in support functions, while microglia are smaller and specialized for immune responses.

Question 12

How do glial scars impact neural recovery?

Answer 12

Glial scars, formed by astrocytes after injury, encapsulate damaged brain areas and prevent axon regrowth, limiting neural recovery in the central nervous system.

Question 13

What are the two main types of glial cells based on size?

Answer 13

The two types are macroglia (larger glial cells like astrocytes and oligodendrocytes) and microglia (smaller immune cells of the CNS).

Question 14

What distinguishes cerebrospinal fluid (CSF) from extracellular fluid (ECF)?

Answer 14

CSF bathes the brain and spinal cord, circulating through the ventricles, while ECF surrounds all cells in the body.

Question 15

What is the role of immunohistochemical identification in neuroscience?

Answer 15

It helps differentiate cell types, including glial cells, by using specific markers expressed on the cell surface or intracellularly.

Question 16

Why does the central nervous system discourage axon regeneration?

Answer 16

Axon regrowth in the CNS is actively inhibited to prevent random, potentially harmful connections that could disrupt the brain’s complex wiring.

Question 17

What are the primary immune mechanisms of microglia?

Answer 17

Microglia detect pathogens, release signaling molecules, transform into phagocytic cells, and engulf harmful debris or damaged cells.

Question 18

How do astrocytes contribute to potassium homeostasis?

Answer 18

Astrocytes express potassium transporters that take up excess potassium from the extracellular fluid, maintaining ionic balance.

Question 19

What is neurovascular coupling, and how are astrocytes involved?

Answer 19

Neurovascular coupling is the regulation of blood flow in response to neuronal activity. Astrocytes modulate this by connecting neurons to capillaries and transferring energy substrates like lactate.

Question 20

What is the significance of GFAP in identifying astrocytes?

Answer 20

GFAP (glial fibrillary acidic protein) is a marker commonly used to identify astrocytes in immunohistochemistry.

Question 21

What process allows astrocytes to influence a large number of synapses?

Answer 21

Astrocytes extend long processes that can contact and regulate up to 1,000 synapses, impacting neurotransmission and maintaining synaptic microenvironments.

Question 22

What role does myelination play in axon function?

Answer 22

Myelination insulates axons, preventing electrical signal loss and allowing faster propagation of action potentials.

Question 23

How do microglia respond to ATP in the extracellular fluid?

Answer 23

ATP in the extracellular fluid signals potential damage or danger, activating microglia to initiate repair processes or immune responses.

Question 24

What are reactive microgliosis and neuroinflammation?

Answer 24

Reactive microgliosis is the activation of microglia in response to injury or infection. Neuroinflammation involves the release of immune and inflammatory molecules in the CNS.

Question 25

How do oligodendrocytes differ from Schwann cells in terms of their myelination patterns?

Answer 25

Oligodendrocytes myelinate multiple axons in the CNS, while Schwann cells myelinate only a single axon in the PNS.

Question 26

Why is the blood-brain barrier relevant to microglial function?

Answer 26

The blood-brain barrier restricts immune cells like white blood cells from entering the brain, leaving microglia as the primary immune defense in the CNS.

Question 27

What is the importance of astrocytic lactate production?

Answer 27

Astrocytes convert glucose into lactate and supply it to neurons as an energy source during high activity or metabolic stress.

Question 28

What is the role of ciliated ependymal cells in the brain?

Answer 28

Ciliated ependymal cells help circulate cerebrospinal fluid through the ventricles, facilitating its movement and distribution.

Question 29

What is the relationship between astrocytes and neurotransmitter clearance?

Answer 29

Astrocytes express uptake transporters to remove excess neurotransmitters from the extracellular fluid, preventing unwanted signaling and maintaining synaptic specificity.

Question 30

What are lipopolysaccharides (LPS), and how do they interact with microglia?

Answer 30

LPS are components of bacterial cell walls that activate microglia, signaling the presence of a pathogen and triggering an immune response.

Question 31

What are the two primary categories of glial cells?

Answer 31

Glial cells are categorized as macroglia (e.g., astrocytes, oligodendrocytes) and microglia based on their size and functions.

Question 32

What is the functional difference between central and peripheral nervous systems regarding axon regeneration?

Answer 32

Axon regeneration is actively encouraged in the peripheral nervous system by Schwann cells, while it is inhibited in the central nervous system by oligodendrocytes and glial scars.

Question 33

What role do ependymal cells play beyond producing cerebrospinal fluid (CSF)?

Answer 33

Ependymal cells help move CSF through the brain’s ventricles using their cilia, though the exact control mechanisms of CSF movement remain unclear.

Question 34

Why is the study of glial cells gaining increased interest in neuroscience?

Answer 34

Glial cells are now recognized as critical for brain function, including roles in synaptic transmission, energy support, immune response, and potential therapeutic targets for brain disorders.

Question 35

How do astrocytes maintain the microenvironment of synapses?

Answer 35

Astrocytes regulate ion concentrations, uptake excess neurotransmitters, and isolate synapses to prevent signal interference from neighboring synaptic activity.

Question 36

What is the role of astrocytes in neural development?

Answer 36

Astrocytes provide scaffolding for neuronal placement and connections during brain and spinal cord development.

Question 37

How do astrocytes influence blood flow in the brain?

Answer 37

Astrocytes connect to capillaries and neurons, modulating blood flow based on neuronal activity to ensure adequate energy supply, a process known as neurovascular coupling.

Question 38

What unique property of astrocytes allows them to form large communication networks?

Answer 38

Astrocytes are interconnected through gap junctions, enabling them to transmit signals and maintain coordination over large brain areas.

Question 39

How do microglia detect and respond to pathogens?

Answer 39

Microglia have receptors that recognize pathogen-associated molecules, such as lipopolysaccharides (LPS) from bacterial walls, and initiate immune responses.

Question 40

What is the function of potassium transporters in astrocytes?

Answer 40

Potassium transporters in astrocytes prevent extracellular potassium buildup during intense neuronal activity, maintaining ionic homeostasis.

Question 41

Why are astrocytes referred to as “metabolic helpers” of neurons?

Answer 41

Astrocytes supply neurons with lactate, derived from glucose, to sustain energy levels during high activity.

Question 42

What is reactive microgliosis?

Answer 42

Reactive microgliosis is the activation and transformation of microglia in response to injury, infection, or disease in the central nervous system.

Question 43

How do microglia contribute to neurodegenerative diseases?

Answer 43

Chronic activation of microglia can lead to the release of neurotoxic substances and phagocytosis of healthy neurons, contributing to diseases like Alzheimer’s and Parkinson’s.

Question 44

How do astrocytes respond to cellular injury in the brain?

Answer 44

Astrocytes detect ATP and glutamate released from damaged cells, proliferate, and form glial scars to isolate the damaged area.

Question 45

What are glial scars, and what is their function?

Answer 45

Glial scars, formed by astrocytes, encapsulate damaged brain tissue to prevent the spread of injury but inhibit axon regrowth.

Question 46

What are some emerging therapeutic applications of targeting glial cells?

Answer 46

Glial cells are being explored as targets for treating brain disorders, enhancing neuroprotection, and promoting controlled regeneration in the CNS.

Question 47

What challenges delayed the study of glial cells historically?

Answer 47

Glial cells lack electrical excitability and were not detectable by early electrophysiological techniques, leading to a focus on neurons.

Question 48

What are potential subtypes of astrocytes, and why are they significant?

Answer 48

Astrocytes likely have multiple subtypes with distinct functions, similar to neurons, though their classification is still under research.

Question 49

Why is there no regeneration of nerves in the central nervous system?

Answer 49

CNS regeneration is prevented by a lack of endoneurial tubes, inhibitory signals from oligodendrocytes, and glial scar formation.

Question 50

What is the significance of blood oxygen level-dependent (BOLD) imaging?

Answer 50

BOLD imaging measures brain activity indirectly by detecting changes in blood flow driven by astrocyte-neuron interactions.