Glial Cells (Theme A) Flashcards
(39 cards)
What are the 2 main types of cells in the NS?
Neurones & glial cells
Which type of cells, neurones or glia are electrically excitable and can conduct APs?
Neurones
What is the correlation between glial number and computational power?
There is a correlation between increased glial number and increased computational power
(*correlation does not equal causation)
How do glial cells differ between humans and mice?
Humans have both more glia and more complex glia
Does this provide further evidence for the correlation between increased glia and increased computational power?
Give 5 examples of GLIOTRANSMITTERS
Glutamate
d-serine
ATP / adenosine
TNFa
BDNF
What is one major side effect of marijuana intoxication?
Memory impairment
Name 2 ways that astrocytes communicate with each other
- Gap junctions (Ca2+ waves)
- Gliotransmitters
Neurones & glia are ____________ throughout the CNS & PNS
Intimately intermixed
Compare the number of neurones and number of glial cells
Number of glial cells > number of neurones
Relative number of glial cells is larger in the PNS
What are the 3 types of glial cells?
What do they do?
- Oligodendrocyte (CNS) / Schwann cells (PNS) - make myelin
- Astrocytes - end-processes envelop blood vessels & synapses
- Microglia - involved in immune response
Describe how glial cells (astrocytes) modulate synaptic function
- Many synapses in the brain are enveloped by astrocyte end-processes
- NT diffuses into the synaptic cleft & binds to receptors on astrocytes
- Causing inc [Ca2+] in astrocytes, stimulating them to release GLIOTRANSMITTERS (signalling molecules)
- Gliotransmitters modulate (up / down-regulate) synaptic transmission by acting on the pre- or post- synaptic site
What is the name of the synapse model that accounts for both NTs & Gliotransmitters?
The Tripartite Synapse
Where are Cannabinoid type-1 receptors (CB1R) found in the brain?
Found on both neurones & glial cells
(One of the most abundant GPCRs in the brain)
What particular synapse, involved with Cannabis use, is an example of the modulation of synaptic function by astrocytes?
The CA3-CA1 synapse in the hippocampus (major involvement in memory)
Describe the process of astrocyte action in the CA3-CA1 synapse in the hippocampus
- Cannabinoids bind to CB1Rs on astrocytes, inc intracellular [Ca2+] -> causing glutamate release
- Glutamate released from astrocytes binds to NMDA receptors on postsynaptic membrane (on the side near the glial cell)
- This inhibits the (glutamate) AMPA receptor, through stimulating endocytosis of AMPA receptors - so glutamate released from the presynaptic neurone can’t bind
- This reduces depolarisation, making the synapse ineffective
- Causing memory impairment associated with cannabis use
How do glia maintain homeostasis in the extracellular space?
Re-uptake of excess NT into glial cell via NT transporters, where it is recycled / metabolised
Balancing of ions - e.g., K+ buffering: K+ diffuses out of extracellular space into glial cell via K+ channels. This is useful as accumulation of extracellular K+ can cause conduction block
Describe how astrocytes shift blood flow to active areas
- Astrocyte end feet / processes envelop blood vessels
- NT (e.g., glutamate) binds to astrocyte receptors at the synapse -> increasing intracellular [Ca2+] in the astrocyte
- This stimulates the astrocyte to release vasoactive molecules (act on blood vessels) - particularly metabolites of arachindonic acid (e.g, prostaglandins)
- This causes the blood vessel to dilate
What are the 3 different functional states of microglia?
- Surveillance (‘resting’) state - cell bodies are stationary, but processes are constantly moving, monitoring brain tissue
- Activated state - following a disturbance of brain homeostasis, they secrete bio-active substances (e.g., cytokines)
- Phagocytic state - act as phagocytes - clump around cells & engulf them
At what point is there a particular wave of synapse formation?
During development
What happens to synapses in adolescence?
- There is competitive elimination of synapses (‘pruning’)
- Synaptic pruning eliminates weaker synapses
- Experience determines pruning: synapses that have been activated most frequently are maintained
What experiment set-up provides evidence that synapse formation is controlled by signals from glial cells (astrocytes)?
In mixed neurone-glia cultures, synapses form readily
But in pure neuronal cultures, very few synapses form
CNS glial cells control the formation of correct brain circuits through controlling the formation & elimination of synapses. Which glial cells promote synapse formation, and which promote synapse elimination?
Astrocytes promote synapse formation
Microglia eliminate synapses
Synapse number is a key feature in neurological disease & aging. Which conditions have reduced synapse numbers? Which conditions have increased synapse numbers?
Reduced synapse numbers in: old age, dementia, AD, Schizophrenia
Increased synapse numbers in: epilepsy, autism
*raises the question - do the glial mechanisms that control synapse numbers in development, fail in aging & disease, causing abnormal synapse numbers?
Give 4 examples of adult diseases with associated neuronal death
ALS (motoneurone disease)
PD
AD
Huntington’s Disease
