Glia Flashcards
What are the basic functions of glia in the brain?
Physical support
Metabolic support
Electrical insulation
Guiding connections
How are glia cells identified?
Morphology - shape
Expression specific markers
Immunohistochemical identification
What are the glia cell types?
Macroglia:
Schwann cells - in periphery
Oligodendrocytes - CNS These 2 form myelin
Ependymal cells
Astrocytes
Microglia
What are Schwann cells?
Myelin-forming cells in the PNS.
Projects the cell membrane which wraps around the axon to form a myelin covering, and Nodes of Ranvier in between.
Provides electrical insulation for the action potential so it can propagate down the axon rather than leaking out.
What are oligodendrocytes?
Myelin-forming cells in the CNS.
One cell can myelinate up to 30 axons.
Actively discourage regrowth of a damaged axon.
What do Schwann cells do with damaged axons?
Encourage regeneration of dead or damaged axons in the PNS.
This is due to endoneurial tube, which is not present in the CNS.
(compared to oligodendrocytes which discourage in the CNS).
What are ependymal cells?
Form the walls of the ventricles of the brain and spinal cord - fluid-filled spaces.
Involved in production of cerebrospinal fluid.
The ciliated cells help circulate CSF.
What are astrocytes form?
Largest and most numerous glial cell type.
Stellate (star like) morphology.
Processes can be very long.
Can look like dendrites.
What is the function of astrocytes?
Neuronal guidance during development.
Forms the architecture of brain and spinal cord.
Astroglia stem cells - adult neurogenesis - making new neurons - and gliogenesis - making new glia.
What are astrocytic syncitium?
Large networks of astrocytes.
Connected through gap junctions (electrical synapses).
Physically and electrically connected.
Allows communication over large spaces.
How are astrocytes used in homeostatic mechanisms?
K+ buffering in ECF.
Express transporters to take up K+ ions.
This prevents accumulation of K+ resulting from neuron firing.
How do astrocytes control the synapse?
If a neuron releases too much neurotransmitter, it can diffuse away from the synapse - to Extracellular space and interact with other neurones.
Express neurotransmitter transporters.
Prevent diffusion outside of synapse - protected microenvironment.
How do astrocytes protect the synapse?
Express various transporters to prevent entry from outside the synapse.
Protects the synapse from the extracellular fluid.
How are astrocytes involved in neurovascular coupling?
‘Foot’ processes envelop capillaries and neurons.
Can modulate cerebral blood flow.
Provides energy to the neuron.
Important for highly active neurons.
Can transport food sources from the blood to the neurone:
takes up glucose from blood, converts to lactate, and neurone takes up and converts to glucose as an energy source.
How do astrocytes respond to insult?
Damaged cells release ATP and glutamate.
Astrocytes respond to increased ATP by Astrocyte hypertrophy (increase in size) and proliferation = reactive astrogliosis - increased GFAP expression.
Form glial scars around injured CNS.
Produce inhibitory molecules that inhibit growth of damaged or severed axons.
What are microglia?
Immune competent cells in the CNS.
Respond to damaged neurones and invading pathogens.
Arise from bone marrow monocytes.
Migrate to nervous system during development.
What is the function of microglia?
In adults, motile processes monitor environment.
Danger signals or injury trigger transformation.
CNS immune system and injury defence/repair.
Reactive microgliosis.
What is microglial activation?
Express immunological and neurotransmitter receptors.
Activation stimuli - tissue injury, pathogen-derived triggers - viral coat proteins and lipid polysaccharide (bacterial cell wall), neuronal signalling.
What is the neuroinflammatory response of microglia?
Proliferation
Release of pro-inflammatory signalling substances e.g. nitric oxide, cytokines - TNFa, IL-1B.
How can microglia be linked to CNS disorders?
Activated microglia can be neurotoxic - astrocyte activation.
Long-lasting microglial activation is linked to pathological processes.
Possible involvement in Alzheimers and Parkinsons, and ischaemic brain damage.
