Glial cells Flashcards
what are the four main functions of glial cells?
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
what three key roles of microglia only recently discovered in the past few decades?
- 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
who named neuroglia and why?
Virchow in 1856 means nerve glue in german
what are satelitte cells
- surround neuron cell bodies in ganglia
- regulate O2, CO2, nutrient and neurotransmitter levels around neurons in ganglia
- PNS
Describe Schwann cells
- surround axons in the PNS
- responsible for myelination of peripheral axons
- participate in repair process after injury
name all the neuroglia and where they act?
PNS:
satellite cells
schwann cells
CNS:
oligodendrocytes
ependymal cells
microglia
astrocytes
Describe process of conception to adulthood in regards to brain processes
1) neurogenesis
2) neuronal migration
3) glialgenesis
4) synaptogenesis
5) myelination
6) synaptic pruning
Name two things that occur by 6 weeks of gestation
- vaculogenesis in the telencephalic wall
- endothelial blood brain barrier formation
what are radial glia?
- 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
what is the common cell that can give rise to astrocytes and oligodendrocytes?
O2A progenitor
what cells give rise to schwann cell precursors?
neural crest cells
what can neural crest cells give rise to ?
- schwann cell precursors
- peripheral sensory and autonomic neurones
- satellite cells of the dorsal root ganglia
what do immature schwann cells differentiate into and why?
myelinating or non-myelinating depending on early association with large or small diameter axons
whats the difference between oligodendrocytes and astrocytes
the stages of astrocyte lineage development are poorly defined, lacking stage-specific markers and clearly defined endpoints
what is required in the pathway from neural stem cell to astrocyte?
neural stem cell to astrocyte precursor (specification requires Sox9, NFIA)
astrocyte precursor to astrocyte (differentiation requires JAK/ STAT, gp130, STAT3)
what are the four basic characteristics of microglial population?
- 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
what are three functions of astrocytes?
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
what is a tripartite synapse?
a concept in synaptic physiology based on the demonstration of the existence of bidirectional communication between astrocytes and neurons
evidence for tripartite synapses?
- 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
further evidence for tripartite synapses (astroccyte exxcitability)?
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
further evidence for tripartite synapses (communication)?
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
what is the blood brain barrier?
- 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
where is the biggest difference in microglia morphology?
between grey (ramified) and white (bipolar) matter
what does microglias immune sensors and reactants allow for?
rapid and plastic reactions to disruptions of the brains homeostasis
where are erythromyeloid progenitors derived from?
the yolk sac which gives rise to all macrophage populations
what three enviromental factor s play fundamental roles in shaping, maintaining and reinforcing microglial identity?
CSF1, IL34 and TGFB
what is myelination dependant on?
axonal diameter
name a all myelinating cell?
oligodendrocytes
- in the CNS
- each myelinating multiple axons (average ~ 10 axons per cell)
what do schwann cells do in terms of myelination?
can be myelinating and non-myelinating
- myelinating schwann cells wrap single axons
what are nodes of ranvier?
specialised naked axonal areas where action potentials are propogated
- myelin sheath between nodes is called internodes
what is the pathiophysiology of MS (Multiple Sclerosis)?
- 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
