Glial Cells Flashcards
What are the different types of glial cells?
Astrocytes
Oligodendrocytes
Microglia
What is the most common type of glial cell?
Astrocytes
What are the functions of astrocytes?
Give structural support to neurones
Contribute to nutrition of neurones
Remove neurotransmitters
Maintain ionic environment
Contribute to blood brain barrier
What do neurones metabolise?
Glucose
How is glucose transported into neurones?
Diffuses from the blood into the interstitial space in the brain through a GLUT transporter
Diffuses from the interstitial space into the neurone through another GLUT transporter
How do astrocytes contribute to nutrition of neurones?
Astrocytes store glucose as glycogen
Glucose-lactate shuttle
What is the glucose-lactate shuttle?
In times of increased neuronal metabolism, astrocytes produce lactate from glycogen
Lactate is transported from the astrocyte into the interstitial fluid and then into the neurone using transporters
In neurones, lactate is converted into pyruvate and then metabolised as normal
Why do astrocytes remove neurotransmitters?
To end the response
To prevent spread of neurotransmitter and stimulation of other post-synaptic neurones
Because some neurotransmitters e.g. glutamate are toxic to neurones at high concentrations
What do astrocytes do with glutamate?
Convert it into glutamine
What happens to glutamine in astrocytes?
Transported back to pre-synaptic neurone
Converted back into glutamate
How do astrocytes maintain the ionic environment?
Na+ K+ ATPase on astrocyte membranes moves potassium ions into astrocytes
Also they have a very negative resting membrane potential
So potassium ions move down their electrical gradient into astrocytes
Why is it important that astrocytes maintain the ionic environment?
Highly active neurones may result in an increase in extracellular potassium ion concentration
This results in depolarisation of neurone membranes, action potentials etc.
What is the function of oligodendrocytes?
Myelinate neurone axons in the CNS
One oligodendrocytes can myelinate multiple neurone axons
What is the structure of a microglial cell?
Small cell body
Many fine processes
When activated, have a more rounded shape
What is the function of microglial cells?
Recognise foreign material or debris
Become activated and phagocytose the substance
What is the blood-brain barrier made up of?
Continuous capillaries
Surrounded by end feet of astrocyte processes
What are continuous capillaries made up of?
Endothelial cells with tight junctions in between them
Complete basement membrane around them
How do astrocytes contribute to the blood-brain barrier?
Promote formation of tight junctions between endothelial cells
What is the function of the blood-brain barrier?
Controls passage of substances from the blood to the extracellular fluid to the brain
Allows for maintaining the correct environment for neurones
What substances can pass across the blood-brain barrier themselves?
Lipophilic substances passively diffuse across the blood-brain barrier e.g. oxygen, carbon dioxide, water
What substances cannot pass across the blood-brain barrier themselves? How do they pass across it then?
Large and hydrophilic substances e.g. glucose, amino acids, ions
Have to be transported across
Why is it important to maintain the correct environment for neurones?
Potassium ion concentration affects resting membrane potential of neurones
Amino acid levels affect neurotransmitter function in synapses
What is immune privilege?
Refers to a type of immune specialisation
Where antigens can be tolerated by T cells without stimulating an inflammatory response
Where does immune privilege occur in the body?
The brain
Why does immune privilege occur in the brain?
Brain is enclosed in the skull which is rigid
Swelling due to inflammation would lead to raised intracranial pressure and brain compression or herniation
