Neurons and Astrocytes Flashcards
Difference between PNS and CNS neurons
Peripheral neurons (PNS): cell bodies outside brain/spinal cord
Central neurons (CNS): cell bodies inside brain/spinal cord
Describe events of AP generation
- Na/K pump maintain RMP (-70)
- Ligand gated Na channel open
- Na influx -> depolarisation (>55)
- Fast Na channel open, slow K channel open
- depolarisation
- Na close as K open (K efflux)
- RMP, K channel slow to close (hyperpol + refractory period)
- Na/K pump restores RMP
Name 2 main compartments in neurons (that must be kept separate)
Axonal compartment and somato-dendritic compartment
E.g. of somato-dendritic specific component?
Microtubule Stabilising Protein: MAP2B
Main advantages of a neuron having dendrites?
Greatly increased surface area
How to distinguish between axons and dendrites?
Axons have no spines
Primary dendrites VS secondary dendrites?
Primary dendrites branch directly off soma, whilst secondary dendrites branch off other dendrites
E.g. of axon specific component?
- neurofilaments (for strength)
- MTs (microtubules)
- tau (to stabilise MTs)
- cell-adhesion molecules (L1-NgCAM, TAG-1)
- NTs, SNARE complexes, growth factor receptors…etc
Why do axons have large numbers of mitochondria?
To maintain membrane potential
Types of synapses (not boutons & varicosities)
- w/ another neuron
- neuromuscular
- neuroglandular
Features of synapses (to aid function)
- enriched w/ VGCCs (calcium channels)
- abundant mitochondria
- synaptic vesicles
- “active zone” (aids vesicle association w/ membrane)
Where on an axon, is the axon potential generated?
Axon hillock
General function of synapses
axo-dendritic:
axo-somatic:
axo-axonic:
General function of synapses
axo-dendritic: excitatory
axo-somatic: inhibitory/modulatory
axo-axonic: inhibitory/modulatory
Main components of astrocytic cytoskeleton?
- GFAP (glial fibrillary acidic protein)]- important
- microtubules
- actin
Unique features of astrocytes
- cytoskeleton has particular proteins (GFAP)
- express vimentin
- glycogen granules
- large nucleus
- light cytoplasm
Examples of structures that astrocytes interact with
- capillary endothelial cells
- neuronal cell bodies
- initial segment
- axon
- dendrites
- synapses
- ependymal cells
- pial surface of brain
Types of astrocytes
- fibrous (long processes)
- protoplasmic (short processes)
Where are astrocytes located?
- Grey matter: protoplasmic, close to neurons]- low GFAP
- White matter: fibrous, alongside neurons]- high GFAP
- Cerebellum
- SVZ]- high GFAP
Functions of astrocytes?
- modulate synaptic function: synaptogenesis (recycles glutamate) and synaptic pruning
- produces cholesterol
- maintain BBB (end feet wrap around endothelial cells)
- regulate blood flow
- neuroprotective (releases growth factors)
- recycles NTs
- produces anti-inflammatory cytokines
Types of astrocytic dysfunction, leading to neurotoxicity
- increased glutamate toxicity
- increased Ca and ATP release
- increased nitric oxide production
- accumulation of superoxide dismutase
- glial scar formation (e.g. around amyloid plaques)
“States” of astrocytes?
A1: bad, reactive
A2: good
Astrocyte role in the BBB?
Astrocytic end feet wrap around endothelial cells, providing gateway for nutrients and removal of metabolites for CNS
Main feature of astrocytic end feet
Contain aquaporin 4
Role of AQP4?
- regulating extracellular space volume
- potassium buffering
- CSF circulation
- interstitial fluid absorption
- metabolic waste (e.g. amyloid) clearance
- neuroinflammation
- osmosensation
- cell migration
- Ca2+ signalling
What is synaptic pruning?
Phagocytosis of unused synapses
Mechanisms of astrocytic NT recycling?
Astrocytic processes surrounding synapse endocytose unbound GABA/glutamate
GABA -> glutamate
Glutamate -> glutamine
Glutamine is resupplied to neuron
Describe mechanism of “spatial buffering” of potassium
Astrocytes act as potassium reservoir
[kept away from extracellular space until needed]
Extracell potassium must be low to allow neuronal function
After intense neuronal activity, potassium conc. can be very high
Astrocytes redistribute potassium to other regions through astrocytic network and gap junctions = spatial buffering
Describe metabolic functions of astrocytes
- produce lactate from glycogen: energy for neurons
- produce cholesterol: brain is most cholesterol-rich organ and relies on this
- Apolipoprotein E
Describe structural role of astrocytes
In radial glia:
Span cortex radially from inner->outer layers
This is important for neuronal migration
e.g. Bergmann glia (cerebellum) and Muller cells (retina)
Describe astrocytic role regarding neural stem cells
Radial glia can give rise to neurons, astrocytes and ependymal cells- multipotential
Mature astrocytes seem to have capacity to form neurons
