Glial cells

Question 1

what are the four main functions of glial cells?

Answer 1

1) to surround neurons and provide physical support (hold them in place)
2) to supply nutrients and oxygen to neurons
3) to insulate one neuron from another and facilitate synaptic communication
4) to destroy and remove cell debris and unwanted molecules

Question 2

what three key roles of microglia only recently discovered in the past few decades?

Answer 2

• developmental roles, in guiding migration of neurons in early development and producing molecules that modify the growth of axons and dendrites
• active participants on synaptic transmission, regulating clearance of neurotransmitters from synaptic cleft, releasing factors such as ATP which modulate presynaptic function and releasing neurotransmitters themsleves
• fundamental role in brain disease and degeneration defining the pathophysiological trajectory

Question 3

who named neuroglia and why?

Answer 3

Virchow in 1856 means nerve glue in german

Question 4

what are satelitte cells

Answer 4

• surround neuron cell bodies in ganglia
• regulate O2, CO2, nutrient and neurotransmitter levels around neurons in ganglia
• PNS

Question 5

Describe Schwann cells

Answer 5

• surround axons in the PNS
• responsible for myelination of peripheral axons
• participate in repair process after injury

Question 6

name all the neuroglia and where they act?

Answer 6

PNS:
satellite cells
schwann cells

CNS:
oligodendrocytes
ependymal cells
microglia
astrocytes

Question 7

Describe process of conception to adulthood in regards to brain processes

Answer 7

1) neurogenesis
2) neuronal migration
3) glialgenesis
4) synaptogenesis
5) myelination
6) synaptic pruning

Question 8

Name two things that occur by 6 weeks of gestation

Answer 8

• vaculogenesis in the telencephalic wall
• endothelial blood brain barrier formation

Question 9

what are radial glia?

Answer 9

• differentiate from neural progenitors early in development, with somata in the ventricular zone and extending prolongations to the pia
• give rise to all cell lineages, contributing to populate the brain and providing a scaffold for neuronal migration

Question 10

what is the common cell that can give rise to astrocytes and oligodendrocytes?

Answer 10

O2A progenitor

Question 11

what cells give rise to schwann cell precursors?

Answer 11

neural crest cells

Question 12

what can neural crest cells give rise to ?

Answer 12

• schwann cell precursors
• peripheral sensory and autonomic neurones
• satellite cells of the dorsal root ganglia

Question 13

what do immature schwann cells differentiate into and why?

Answer 13

myelinating or non-myelinating depending on early association with large or small diameter axons

Question 14

whats the difference between oligodendrocytes and astrocytes

Answer 14

the stages of astrocyte lineage development are poorly defined, lacking stage-specific markers and clearly defined endpoints

Question 15

what is required in the pathway from neural stem cell to astrocyte?

Answer 15

neural stem cell to astrocyte precursor (specification requires Sox9, NFIA)

astrocyte precursor to astrocyte (differentiation requires JAK/ STAT, gp130, STAT3)

Question 16

what are the four basic characteristics of microglial population?

Answer 16

• ramified morphology, tiling the brain parenchyma in a mosaic-like distribution
• biggest differences in morphology between grey (ramified) and white (bipolar) matter
• variable densities in different regions, with each cecll covering an average volume of 50000um3
• equipped with a repertoire of immunen ‘sensors’ and ‘reactants’, allowing rapid and plastic reactions to disruptions of the brains homeostasis

Question 17

what are three functions of astrocytes?

Answer 17

1) neurogenesis and gliogenesis in the adult brain
2) neuronal guidance in development: role of radial glia
3) regulation of synaptogenesis and synaptic maturation in development
4) structural function: forming microarchitecture of the brain and communication through gap junctions
5) creation of the blood brain barrier
6) synaptic modulation

Question 18

what is a tripartite synapse?

Answer 18

a concept in synaptic physiology based on the demonstration of the existence of bidirectional communication between astrocytes and neurons

Question 19

evidence for tripartite synapses?

Answer 19

• 60% of axon-dendritic synapses surrounded by astroglial membranes (hippocampus)
• 80% of large perforated synapses are enwrapped by astrocytes
• In the cerebellum, interaction of purkinje cells with bergmann cells (which are the astrocytes of the cerebellum) each cell enwrapping 2000-6000 synaptic contacts

Question 20

further evidence for tripartite synapses (astroccyte exxcitability)?

Answer 20

astrocytes are excitable cells:
- in response to presynaptic or postsynaptic stimulation astrocytes are capable of producing transient changes in their intracellullar calcium concentrations through release of calcium stores from the ER

Question 21

further evidence for tripartite synapses (communication)?

Answer 21

astrocytes communicate bidirectionally with neurons
- able to detect neurotransmitters and other signals released from neurons at the synapse and can release their own neurotransmitters or gliotransmitters
- that in turn are capable of modifying the elctrophysiological excitability of neurons

Question 22

what is the blood brain barrier?

Answer 22

• barrier between the intracerebrakk blood vessels and the brain parenchyma
• formed by tight junctions between endothelial cells and astroglial endfeet
• present throughout the brain except in circumventricular organs, neurohypophysis, pineal gland, subfornical organ and lamina terminalis, involved in neuroendocrine signalling

Question 23

where is the biggest difference in microglia morphology?

Answer 23

between grey (ramified) and white (bipolar) matter

Question 24

what does microglias immune sensors and reactants allow for?

Answer 24

rapid and plastic reactions to disruptions of the brains homeostasis

Question 25

where are erythromyeloid progenitors derived from?

Answer 25

the yolk sac which gives rise to all macrophage populations

Question 26

what three enviromental factor s play fundamental roles in shaping, maintaining and reinforcing microglial identity?

Answer 26

CSF1, IL34 and TGFB

Question 27

what is myelination dependant on?

Answer 27

axonal diameter

Question 28

name a all myelinating cell?

Answer 28

oligodendrocytes
- in the CNS
- each myelinating multiple axons (average ~ 10 axons per cell)

Question 29

what do schwann cells do in terms of myelination?

Answer 29

can be myelinating and non-myelinating
- myelinating schwann cells wrap single axons

Question 30

what are nodes of ranvier?

Answer 30

specialised naked axonal areas where action potentials are propogated
- myelin sheath between nodes is called internodes

Question 31

what is the pathiophysiology of MS (Multiple Sclerosis)?

Answer 31

• BBB breakdown: damaged BBB drives the entrance of T Cells predominately (and other immune cells)
• Chronic inflammation: demyelination triggered by T cells attacking myelin, driving recruitment of other inflammatory cells by releasing cytokines and antibodies
• BBB leakage causes swelling, activation of macrophages and a vicious cycle of inflammation and damage driven by astrocytes and microglia