L2 - Glial cells Flashcards
what is the difference between glial cells and neurones?
neurones are electrically excitable and generate APs
glial cells are not electrically excitable, they are homeostatic cells of the nervous system
why are glia not elecrically excitable?
few voltage gated channels
what types of glial cells are found in the CNS
macroglia
- astrocytes
- oligodendrocytes
- NG2 glia
microglia
what is the origin of macro glia? what are examples of macro glial cells (3)
neural origin (ectodermal) (neuroepithelium)
astrocytes
oligodendrocytes
NG2 glia
what is the origin of microglia
non neural origin , mesodermal
what types of glial cells are found in the PNS
schwann cells
enteric glia (GI tract)
satelite glial cells
olfactory ensheathing cells
what are satellite glial cells
glial cells of sensory and sympathetic ganglia
what different types of schwann cells are there?
non myelinating
myelinating
perisynaptic
describe some properties of astrocytes
long branching star-like processes contain GFAP (glial fibrillary acidic protein)
where do astrocyte processes contact
nodes of ranvier
what are the two main types of true astrocyte
fibrous astrocytes
protoplasmic astrocytes
where are protoplasmic astrocytes found
grey matter
where are fibrous astrocytes found
white matter
fucntions of astrocytes
structural support
form surface under the pia (glia limitans)
form signalling and transport pathway between neurones and blood vessels
inhibit regeneration in CNS
enwrap BBB
encase dendrites of CNS neurones
NT uptake
how do astrocytes provide structural support
their expression of intermediate filaments
how do astrocytes form signalling and transport pathway between neurones and blood vessels
there is an astrocyte between every brain capillary and neurone
describe organisation of astrocyte-neuronal network
a single astrocyte will contact multiple dendrites of one neurone
each neurone has multiple astrocytes that its in contact with
astrocytes do not overlap
how many axons can an oligodendrocyte myelinate
up to 30-50
function of oligodendrocytes
wrap around axons forming myelin sheaths
what are NG2 glia?
group of cells of the CNS that express neurone antigen 2
where do NG2 glia originate from
oligodendrocyte precursor cells
fucntions of NG2 glia
- form numerous contacts with neurones and receive functional afferents, forming functional synapses
- Able to generate oligodendrocytes during CNS remodelling and following demyelination (serve as multi potent neural stem cells)
function of CNS microglia
immunocompetent cells that form brain immune system activated by injury / disease
what are the three types of CNS microglia
resting
activated
phagocytic
what are schwann cells,
a type of microglia found in PNS
have a role in repair
function of myelinating schwann cells
myelinate peripheral neurones
functiuon of non myelinating schwann cells
ensheath multiple unmyelinated axons
how many axons can a myelinating schwann cell myelinate
1
fucntion of perisynaptic (non myelinating) schwann cells
ensheath terminal axons at the NMJ
what are neural cells of the ectodermal origin derived from
neural epithelium
neuroepithelial cells are pluripotent stem cells
describe the generation of first neurones from neuroepithelial cells
NE cells divide asymmetriclly to form neuronal cells
describe process of oligodendrocyte and astrocyte formation
- NE cells divide symmetrically to form radial cells
- radial cells divide asymmetrically to form neurones, and intermediate progenitor cells for Astrocytes, neurones and oligodendrocytes
what are ependymal cells?
cells classed as astrocytes (in that they arent neurones) but they have microvilli and do not express GFAP
describe the formation (cell lineage) of myelinating schwann cells
- NE cells differentiate into schwann cell precursors, which differentiate into immature schwann cells
- if immature schwann cells come into contact with an axon, they differentiate into pro-myelinating schwann cells
- pro-myelinating schwann cells differentiate into myelinating schwann cells
describe the formation (cell lineage) of non-myelinating schwann cells
- NE cells differentiate into schwann cell precursors, which differentiate into immature schwann cells
- if the immature schwann cells do not come into contact with an axon, they differentiate into non-myelinating schwann cells
what is radial sorting
it determines the differentiation and fate of schwann cells, depends on axonal signalling and axon diameter
what schwann cells (in the lineage) are capable of indefinite differentiation
schwann cell precursors
immature schwwann cells
comment on the differntiation ability of M and non M schwann cells, and why is this important?
they can de-differentiate back into immature schwann cells, and then re-differentiate to either M or non M
gives them regenerative and re-mylination ability
what effect do oligodendrocytes and astrocytes have on nerve regeneration?
they inhibit nerve regeneration
describe microglial cell lineage
- macrophages invade CNS during early foetal development (embryonic period) and give rise to embryonic microglial cells
- (early post partum) microglia precursor cells give rise to amoeboid microglia which proliferate in the corpus callosum then migrate to the brain
- Microglia then rest in brain (ramified) until activated by damage or disease - then form phagocytic type (3 possible states in adult brain)
schwann cell origin
ectodermal (Nueorepithelial cells)
describe electrical synapse (briefly)
passage of ions (and charge) through gap junctions to neighbouring cells
fucntions of astrocytes in synapse (give examples)
can uptake NT (NA/ glutamate / GABA)
can then also release NT (Ca dependant)
briefly comment on the receptor types found on glial cells in different brain regions
glial cells will contain NT receptors for the NT released by neurones that they are located near
define wiring transmission
transmission through chemical / electrical synapses
rapid and local
1:1
define volume transmission
signalling between cells of a further distance via diffusion through extra (or intra) cellular space
slower
1 : many
describe astrocyte ‘excitability’
astrocytes cannot trigger APs but can alter their intracellular [Ca2+] which is how they signal
this is called Ca2+ wave
describe astrocyte signilling via Ca
- NT acting on receptors of astrocytes cause Ca2+ release from ER
- this spreads through the neighbouring cells (Ca2+ wave)
- changes in [Ca] can trigger gliotransmitter release
list the 3 mechanisms of the Ca wave
- Inositol triphosphate mediated Ca2+ release
- gliotransmitter mediated Ca2+ release (local)
- gliotransmitter medicated Ca2+ release volume transmission
describe the inositol triphosphate mediated Ca2+ wave
- Ca2+ release triggered in first cell via InsP3
2. InsP3 diffuses through gap junctions to neighbouring cell and triggers Ca2+ release from ER continuing the wave
describe process of gliotransmitter mediated Ca2+ wave
- Ca2+ increase in the first astrocyte causes gliotransmitter release
- gliotransmitter then binds to receptor on next cell, triggering Ca2+ release (via InsP3) from ER continuing the wave
describe the process of gliotransmitter medicated Ca2+ release volume transmission
same as normal gliotransmitter release wave except the NT acts on further away cells
list gliotransmitters
glutamate
ATP
D-serine
what is Astrocyte roles in homeostasis
K+ buffering (from neuronal activity and APs)
water regulation
pH
PCO2 and PO2 sensors
how do astrocytes buffer K+
they have
inwardly rectifying K+ channels
Na / K+ ATPase pump
Na+ K+ Cl- cotransporter
on their surface that allows K+ to enter astrocytes
Gap junctions allow spatial buffering of K+ into neighbouring actrocytes
K+ is then expelled into interstitium where they then enter blood
where are inwardly rectifying K channels clustered?
perisynaptic processes of astrocytes (near synapses) where neuronal activity is highest
comment on extracellular space around neuronal activity
extracellular space surrounding active synapses shrinks
this increases efficacy of synaptic transmission as [NT] in that area increases (as the area shrinks)
what modulates the shrinkage of the ECM during neuronal activity?
water transport into astrocytes and redistribution via aquaporins
what is the main aquaporin in water transport into astrocytes
aquaporin 4
where are aquaproins clustered
perisynaptic astrocyte processes
describe the process of water transport into astrocytes
- influx of K+ into astrocytes increases osmotic pressure in the astrocyte
- so water flows in
what are the properties of astrocytes that allow K+ buffering
- high K+ conductance (many channels)
2. have a very low resting membrane potential (-90mV)
how do astrocytes regulate pH
- they have a Na / H / HCO3 co transporter that can release HCO3 into ECS which buffers pH
- they have a Na / H antiport to regulate H+ distribution
what are ependymal cells and what is their fucntion
Ciliated cells that line brain ventricles
Produces CSF at the choroid plexus
covered in microvilli to allow absorption of CSF
