The Role Of Neurones And Glia Flashcards
What do neurones do?
Sense changes and communicate with other neurones
What do glial cells do?
Support, nourish and insulate neurones and remove ‘waste’. We have around 10^12 glia
What are the types of glial cells?
Astrocytes (several types) - most abundant, supporters
Oligodendrocytes - insulators
Microglia - immune response
What do astrocytes do?
Structural support
Provide nutrition - via glucose-lactate shuttle
Remove neurotransmitters - control concentration of neurotransmitters (especially important for glutamate as this is toxic)
Maintain ionic environment - K+ buffering
Help form blood-brain barrier
How do astrocytes hep to provide energy for neurones?
Neurones do not store or produce glycogen.
Astrocytes produce lactate which can be transferred to neurones via the glucose-lactate shuttle to supplement the supply of glucose
How do astrocytes help to remove neurotransmitters?
Re-uptake
Astrocytes have transporters for transmitters such as glutamate.
This helps to keep the extracellular concentration of glutamate low.
How do astrocytes help to buffer K+ in the brain?
Astrocytes take up K+ to prevent a rise of K+ in the brain as a result of high levels of neuronal activity.
What are the role of Microglia?
Macrophage of the brain.
Immunocompetant cells.
Recognise foreign material -activated
Phagocytosis to remove debris and foreign material
Brains main defence system.
What is the role of the blood brain barrier?
Limits the diffusion of substances from the blood to the brain extracellular fluid.
Maintains the correct environment for neurones.
Brain capillaries have:
- Tight junctions between endothelial cells
- Basement membrane surrounding capillary
- End feet of astrocyte processes
What substances are allowed to cross the blood brain barrier?
Substances such as glucose, amino acids and potassium are transported across the BBB.
This allows the concentration to be controlled.
How is the immune system different in the CNS?
Does not undergo rapid rejection of allografts.
Rigid skull will not tolerate volume expansion -too much inflammatory response would be harmful.
Microglial can act as antigen presenting cells.
T-cells can enter the CNS.
CNS inhibits the initiation of the pro-inflammatory T-cell response.
Immune privilege is not immune isolation, rather specialisation.
What are three different ways neurones can communicate?
Fast excitatory neurotransmission.
Fast inhibitory neurotransmission.
Modulatory response.
What are the four main sections of a nerve?
Cell soma
Dendrites
Axon
Terminals
What happens at a synapse in the brain?
Depolarisation in the terminal opens VGCC (voltage gated calcium channels). Ca2+ enter the terminal.
Vesicles fuse and release neurotransmitter.
Neurotransmitter diffuses across the synaptic cleft and binds to receptors in postsynaptic membrane.
What does the post synaptic response depend on?
Nature of transmitter.
Nature of receptor -ligand gated or GPCR.
What are some neurotransmitters in the CNS?
Over 30 neurotransmitters have been identified int he CNS. They can be divided into three chemical classes:
Amino acids
Biogenic amines
Peptides
What are amino acid neurotransmitters?
They can be both excitatory or inhibitory depending on the particular amino acid.
Excitatory amino acids:
Mainly glutamate which is the main excitatory neurotransmitter.
–Over 70% of all CNS synapses are glutamatergic.
Inhibitory amino acids:
GABA
Glycine
What are the two types of glutamate receptors?
Ionotropic - Ion channels, permeable to Na+ (sometimes Ca2+).
Activation causes depolarisation -increased excitability.
Metabolic - GPCRs
Linked to either changes in IP3 and Ca2+ mobilisation or inhibition of adenylate cyclase and decreased cAMP levels.
What are fast excitatory responses?
Excitatory neurotransmitters cause depolarisation of the post synaptic cell by acting on ligand-gated ion channels.
Excitatory postsynaptic potential (EPSP)
Depolarisation causes more action potentials.
How do Glutamatergic synapses work?
Glutamatergic synapses have both AMPA and NMDA receptors.
AMPA receptors mediate the initial fast depolarisation.
NMDA receptors are permeable to Ca2+.
NMDA receptors need glutamate to bind and the cell to be depolarised to allow ion flow through the channel. -Also, glycine acts as a co-agonist
Why do glutamate receptors have an important role in learning an memory?
Activation of NMDA receptors (and mGluRs) can up-regulate AMPA receptors.
Strong, high frequency stimulation causes long term potentiation (LTP)
Ca2+ entry through NMDA receptors important for induction of LTP.
Why is too much Ca2+ entry through NMDA receptors bad?
Because it cause excitotoxicity by encouraging too much glutamate.
Excitotoxicity is the pathological process by which nerve cells are damaged or killed by excessive stimulation by neurotransmitters such as glutamate and similar substances.
What are the two inhibitory AA?
GABA - main inhibitory transmitter in the brain.
Glycine - acts as an inhibitory neurotransmitter mostly in the brainstem and spinal cord.
How do GABAa and glycine receptors work?
GABA and glycine receptors have integral Cl- channels.
Opening the Cl- channels causes hyperpolarisation.-Inhibitory post-synaptic potential (IPSP) causes decreased action potential firing.
