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what are the 4 types of glial cells?
- astrocytes
- oligodendrocytes
- microglia
- ependymal cells
what shape are astrocytes?
star shaped
where are astrocytes found?
central nervous system
what percentage of glial cells do astrocytes make up?
20-40%
what are 5 functions of astrocytes?
- provide metabolic support
- regulate extracellular ionic environment
- neurotransmitter uptake
- modulating synaptic transmission
- promotion of myelination by oligodendrocytes
what is the main way that astrocytes provide metabolic support?
they store glycogen which can be broken down into glucose to provide fuel for neurons
what is another way that astrocytes provide metabolic support?
store lactate which is useful in periods of high energy consumption or ischaemia
why is it important for the astrocytes to provide the energy for the brain?
it has a constant requirement for glucose but it is unable to store or produce glycogen itself
why do astrocytes need to regulate the extracellular ionic environment?
high levels of ions like potassium can cause spontaneous depolarisation of the neuron
how do astrocytes regulate the extracellular ionic environment?
they remove excess potassium ions from the extracellular space
how do astrocytes take up neurotransmitters?
contain specific transporters for several neurotransmitters such as glutamate
why do astrocytes need to uptake neurotransmitters?
rapid removal of neurotransmitters from extracellular space is required for normal function of neurons
how do astrocytes modulate synaptic transmission?
release ATP to increase the production of adenosine which inhibits synaptic transmission
what is the main role of oligodendrocytes?
insulating the axons in the CNS
how do oligodendrocytes insulate the axons?
produce a myelin sheath which wraps around the axon
how many axonal segments can a single oligodendrocyte myelinate?
50
what are oligodendrocytes the equivalent to?
Schwann cells in the PNS
what germ layer do astrocytes, oligodendrocytes and ependymal cells arise from?
ectoderm
what germ layer do microglia arise from?
mesoderm
what is the main role of the microglia?
phagocytic and immunocompetent cells
when are the microglia activated?
in response to tissue damage
what happens when microglia are activated?
they can recognise foreign antigens and initiate phagocytosis to remove foreign material
what can microglia also do?
function as antigen presenting cells if needed
what is the ependyma?
thin lining of ventricles in the brain and spinal cord
what is the ependyma made up of?
ependymal cells
what are the ependymal cells attached to?
the basal membrane of the cells is attached to astrocytes
what is the main function of the ependymal cells?
produce cerebrospinal fluid as part of the choroid plexus
what are the ependymal cells covered in?
cilia and microvilli
what do the cilia do?
allow for circulation of CSF
what do the microvilli do?
allow for absorption of CSF