Glia Flashcards
types of vertebrate glial cells
astroglia
microglia
oligodendroglia
Schwann cell
astroglia
- features + functions
star-shaped
symmetrical
common in CNS
nutritive + support function
microglia
- features + function
small
mesodermally-derived
defensive function
- role in breaking down cells + material in brain
= can lead to disease
BUT keeps brain free of pathogens
oligodendroglia
- features + function
asymmetrical
forms myelin around axons in brain + spinal cord (CNS)
Schwann cell
- features + function
asymmetrical
wraps around peripheral nerves to form myelin
classification of cell types
- neural cells
- neuronal cells
- glia
- macroglia
neurones + glia
neurones
microglia + microglia
astrocytes
radial cells
oligodendroglia
Schwann cels
myelinating glia
- 2 types
- function
oligodendroglia
(in CNS)
Schwann cells
(in PNS)
insulates axons
-> increases rate of action potential transfer
radial glia
- function
- produce
provide scaffold throughout CNS for neurones to migrate via during development
matrix + adhesion proteins
radial glia
- in adults
persist as different types of cells
e.g. Muller glia cells in retina
ependymal cells
- structure
lines central canal + ventricles in brain
cuboidal cells but no basement membrane
beating cilia when lining ventricles
ependymal cells
- specialised forms participate in…?
secretion of CSF
= cerebral spinal fluid
origins of cell types
- neurones, astrocytes + oligodendrocytes
- Schwann cells
- microglia
neural tube
neural crest
yolk sac + macrophages (i.e. blood)
gliogenesis
- doesn’t involve..?
microglia
Schwann cells
gliogenesis
- process
neural stem cells
1) -> form neurones
OR
2) -> glial-restricted precursors
A) -> astrocyte precursors
-> type-1 astrocytes
OR
B) ->O2A progenitors
-> forms oligodendrocytes
OR
->type 2 astrocytes
which glia are in the CNS?
astrocyte
oligodendrocyte
microglia
dual origin of microglia
primitive macrophages from yolk sac blood islands migrate into brain
-> eventually become microglia
may come from blood directly
- from monocytes that invade the brain
evidence for monocytic origin of microglia
bone marrow chimeras:
show the brain becomes populated by donor-specific cells of haemopoietic origin
immunocytochemical studies:
show changes in morphology as monocytes transform to microglia
types of microglia
ameboid - round cells clustered - found in development concentrated in corpus collosum - proliferate
ramified
- adult form found in brain
- don’t proliferate when resting
activation states of adult microglia
resting
- fine processes
- OX-42
activated
- thick processes
- larger cell body
- vimentin
- OX-42
- proliferate
- migrate
phagocytic (break down cells)
- globular cell
- lack projections
- vimentin
- OX-42
- OX-8
- proliferate
blood-brain barrier
- define
semipermeable barrier
caused by vasculature + brain cells
prevents passage of cells and large molecules
microglia
- functions
resting cells
- support + protect neurones
- release GFs
antigens activate microglia
-> migrate to antigen
+ secrete toxic substances + pro-inflammatory cytokines
remove damaged neurones
myelin fragments convert to phagocytic state
- consume cell debris from dead neurones
microglial activation sequence
- activation signal
- retraction of extant branches
- motility (protrusion + retraction)
- locomotion
microglia stimulators
viruses + bacteria
dead cells/debris
CNS toxins
ischemia (stroke-related damage)
neuronal degeneration
- release cytokines
activated astrocytes
- release cytokines
controversy:
microglia’s role in neurodegenerative disease
A) certain proteins produced by neurones during these diseases e.g. amyloid
-> activate microglia + kill neurones via ROS production
vs
B) microglia don’t play an active role in killing otherwise healthy cells in brain
- microglia kill damage neurones
astrocytes
- 2 types
- functions
protoplasmic (grey matter)
- maintain blood-brain barrier
- transport K+ and glucose
fibrous (white matter)
- support + structure
- form scar tissue
astrocytes
- ratio of astrocytes:neurones
- perivascular feet
50:1
projections that make contact with blood vessels
astrocyte
- functions
pathways
support
growth + death
calcium signallin g
glutamate
BBB
glucose transport
channels +
receptors
extracellular volume
astrocyte
-pathways
in development
- provide pathways used by neurones to migrate
role in axonal guidance
-involves CAMs, cadherins, integrins, selectins
create boundaries for axonal movement
astrocyte
- support
gives structure and protection to synapse
astrocyte
- growth + death
release large no. of different factors:
GFs + cytokines
= important for survival and development of neurones
astrocytes proliferate around site of axon damage
- could aid repair but can form ‘glial scar’ which inhibits axonal regeneration
astrocyte
- Ca2+ signalling
gap junctions between astrocytes
- allows rapid communication using Ca2+
via calcium waves
- may coordinate synapses into synchronously firing groups
astrocytic regulation of neural networks
all synapses enveloped by an astrocyte may be within that astrocyte’s domain of synaptic influence
-> one group of neurone could influence another distant grip through strictly astrocytic pathways
glutamate
a neurotransmitter
released in excess
- must be removed otherwise excitotoxic death
astrocytes
- glutamate
express glutamate tranporters
= GLAST + GLT-1
-> clear glutamate from synapse
glutamate converted into glutamine + returned to neurones
astrocyte
- BloodBrainBarrier
astrocytes involved in BBB formation
stops immune system cells (e.g. T cells) invading
- provides immune privilege
immunological privilege
rejection of allografts is greatly diminished by transplantation into the nervous system
astrocyte
- K+ and glucose transport
express GLUT
K+ levels for neuronal function
- need to be higher inside neurone
astrocyte
- channels + receptors
neurotransmitter receptors
e.g. seretonin receptor
helps coordinate activity of astrocytes with neurones
ion channels e.g. Ca2+ and K+
- clearance of ions that help maintain levels of ions extracellularly (=interstitial ion levels)
astrocyte
- extracellular volume
astrocytic swelling due to glutamate and adenosine receptor stimulation
volume fraction decreases
-> increased conc of extracellular molecules
(= increases effective cones of neurotransmitters)
astrocytes through modulation of their size can influence excitability of neurones
cytokines
- produced by
- alter
- 2 types of response
- different actions depending on…
astrocytes + microglia
+ neurones
cell survival + proliferation
pro-inflammatory or anti-inflammatory
- point of release
- cells they act on
- concentration
cytokine
- examples
interferons (IFN)
interleukins (IL)
tumour necrosis factor (TNF) family
cytokine
- receptors
microglia, astrocytes + oligodendrocytes express receptors for many cytokines
e.g. microliga express IL-6 receptor
signal transduction mediated by cytokine receptors
- cytokine binds to receptor
- triggers intracellular pathway
e. g. Jak-Stat pathway - stat proteins enter nucleus
- alter transcription
