Astrocytes and oligodendrites Flashcards
What is the most abundant cell in the brain ?
Astrocytes
What are the six functions of astrocytes ?
- neurogenesis and gliogenesis
- neuronal guidance in development
- synaptogenesis and synaptic maturation
- Connect domains
- creation of BBB
- synaptic modulation
What are the two pieces of evidence for tripartite synapses?
- astrocytes are excitable
- communicate bidirectionally with neurones
How are astrocytes excitable?
produce short term changes in intracellular calcium concentration through release of calcium stores from the ER
How do astrocytes communicate bidirectionally with neurones?
Detect NT from neurones
Release their own NT or gliotransmitter = able to modify electrophysiological excitability of neuron
What clearance do astrocytes participate in?
Glu (glutamic acid) clearance by converting it to glutamine
What type of transmitter is Glu?
gliotransmitter
What are the functions of glutamatergic signalling?
Synchronous depolarisation
increase postsynaptic current frequency
AMPA-receptor-dependent postsynaptic current increases
What is the BBB?
barrier between intracerebral blood vessels and brain parenchyma (made of glia and neurones)
Stops entry to brain
The BBB is present throughout the brain apart from which areas?
circumventricular organs (CVOs) neurohypoysis Pineal gland subfornical organs lamina terminals
What junctions form in a BBB?
tight junctions between endo cells and astroglial endfeet
How do solutes cross the BBB?
pass through endothelial cells and mem of astrocytes (selectively permeable to essential nutrients)
Endothelial cells have specific transporters
What are the types of myelinating cells ?
- Oligodendrocytes - all myelinating, CNS, multiple axons
2. Schwann cells - myelinating and non, single axon
What is myelination dependent on ?
Axonal diameter
What is the ratio which is kept constant in the PNS and CNS ?
g-ratio of axons: number of myelin lamellae (1:10)
Explain the interdependence of glia-axons
- Loss of axon = degeneration of oligodendrocytes and de-differentiation of Schwann cells
- Absence of oligodendrocytes = axons degenerate
What do non-myelinating Schwann cells do?
surround small diameter neurones
support and isolation from myelinated axons
express surface markers L1 and NCAM
What do perisynaptic Schwann cells do?
At NMJ
respond to synaptic activity by ca+ waves
Modulate synaptic activity by reg extracellular ion levels and inducing postsynaptic Ach receptor aggregation
What markers do OBECs express?
Glial markers: GFAP, s100, P75
Radial glial markers : nesting and vimentin
What type of conduction does a myelin sheath facilitate?
saltatory conduction
Where are action potentials propagated ?
Node of ranviers
What is the composition of the myelin sheath?
- 70% lipids (mostly cholesterol)
myelin, phospholipids, glycolipids, glycospingolipids - 30% proteins
What is the difference in the composition of the myelin sheath in the CNS and PNS?
CNS= main protein MBP and PLP PNS = main protein P0, PMP22 and Cx32
What is key for saltatory conduction?
molecular interactions at the paranode and juxtaparanode due to clustering of the K+ and Na+ channels
What does the loss of NCAM do?
Neuronal cell adhesion molecule loss from axonal surface triggers myelination
What is L1 ?
Expressed at premyelination
Tags axon to be myelinated
What do oligodendrite precursor cells differentiate into?
Oligodendrocytes starting to express myelin products
What is the function of MAG and PLP in axon ensheathment?
stitch the spirals along the axon
wraps of myelin are fused together by them
What happens to the myelin sheath due to MS?
- autoantibioties of myelin components produced
- involve white matter
- demyelination (by damage to oligodendrocytes)
- BBB breakdown, swelling and inflammation
