2.1.1 Neurones and Glia Flashcards
What do neurones do?
Sense changes and commnicate with other neurones
What do glia do?
Support, nourish and insulate neurones and remove waste
What are the different types of glial cells?
Astrocytes
Oligodendrocytes
Microglia
What do astrocytes do?
- Structural support
- Help to provide nutrition for neurones (glucose-lactate shuttle)
- Remove neurotransmitters (uptake), controls concentration of neurotransmitters
- Maintain ionic environment, K+ buffering
- Helps to form BBB
How do astrocytes help to provide energy for neurones?
Neurones do not store or produce glycogen as they lack the enzymes needed to use glycogen
Astrocytes do store glycogen, they produce lactate which can be transfered to neurones
-Supplements their supply of glucose, can support neurones for a short peirod of time
Describe the glucose lactate shuttle
Glucose enters astrocytes via GLUT1
Glucose then converted into pyruvate, then into lactate
Lactate leaves through MCT1and enters neurone via MCT2, lactate then is converted back to pyruvate generating ATP for the neurone
How do astrocytes remove neurotransmitters?
Astrocytes have transporters for transmitters such as glutamate
Helps to keep the extracellular concentration low, acts to stop depolarisation lasting for long periods of time
Glutamate can be toxic if too high
Why do astrocytes buffer K+ in the brain?
Increased K+ depolaries neurones and can potentially lead to unwanted APs
Astrocytes have a very negatively charged iternal environment therefore K+ ions can move in easily
How do astrocytes buffer potassium ions?
Very negative RMP
K+ enters via NaKATPase, NaK2Cl transports and K+ channels
Lowers the ECF concentration, astrocytes are coupled, K+ can travel between them, concentration does not rise highly in 1 cell
What do oligodendrocytes do?
Myelinate multiple axons in the CNS
What happens in multiple sclerosis?
Autoimmune degeneration of myelin around axons
Oligodendrocytes are also damaged
Less myelination of neurones which slows down the speed of action potential conduction
Can affect any white matter pathway
What do microglia do?
- Immunocompetent cells
- Mesodermal origin
- Recognise foreign material
- Phagocytosis and can act as APCs
- Brains main defence system
How do microglia phagocytose foreign material?
Dendrities swell up until they become phagocytic
Why is the CNS immune priveliged?
If an allograft (cells from someone else) added to brain into does not undergo rapid enjection
Cannot tolerate volume expansion, would compress tissues
What does the blood brain barrier do?
- Limits diffusion of substances form the blood to the brain ECF
- Maintains environment for neurones
How does the blood brain barrier form?
Tight junctions between endothelial cells
Basement membrane surrounding capillary
End feet of astrocyte processes
What substances can freely pass across the BBB?
Lipophilic gases e.g.
-CO2
- O2
- H2O
What substances have to be transported across the BBB?
Glucose
Amino acids
K+
What happens to K+ concentration after intense exercise?
Intense exercise causes K+ concentration to rise
If this got to the brain there would be unwated responses, hence the BBB prevents free movement of K+
Why are amino acids transported across the BBB?
Amino acids can act as neurotransmitters, so if they could pass freely would cause unwated actions of the brain
Why does the brain not have a profound immune response?
Rigid skull
Too much inflammation would be harmful as would compress brain contents
T-cells can enter the CNS but monocytes cannot
CNS inhibits initaiton of pro-inflammatory T-cell response
How does depolarisation occur?
Stimulis received at soma, threshold is reached causing AP to spread down axon
Voltage-gated Na+ channels open and sodium ions enter and depolarise the cell
AP closes Na+ channels, previous parts of the axon are now in the refraction period while RMP is reached
Repolarisation occurs with the opening of K+ channels, K+ leaves the cell
Hyperpolarisation now occurs as K+ channels open, they then close and return to RMP.
What are the 4 sections of a neurone?
Soma (cell body)
Dendrites
Axon
Terminals
What happens at the synapse when depolarisation occurs?
AP travels down axon, depolarisation in the terminal opens voltage-gated Ca2+ ions
Vesicles fuse and release transmitter
Neurotransmitter diffuses across the synpatic cleft and binds to receptors on the postsynaptic membrane
