T1 L20 Plasticity & regeneration Flashcards
What are inducing factors?
Signalling molecule provided by other cells
Freely diffusible, exert action over a long range
Tethered to cell surface acting locally
Modify gene expression, cell shape & motility
What is competence?
Ability of a cell to respond to inducing factors
What does competence depend on?
Exact set of surface receptors
Transduction molecules
Transcription factors expressed by the cell
What is neurogenesis?
Process by which neurons are generated
What are neural stem cells?
(Neural precursor cells)
Infinitely self renewing
After terminal division & differentiation they can give rise to full range of cell cases within relevant tissues
What is a neural progenitor cell?
Unable to continually self-renew Capable to give rise to only one class of differentiated progeny
Give an example of a neural progenitor cell
Oligodendroglial progenitor cell gives rise to oligodendrocytes
Where is the nucleus in G1?
Near the ventricular surface
Where is the nucleus in S?
Migrate toward pial surface & DNA replicates
What happens in G2?
Cell grows & nucleus migrates towards lumen
What happens if there is a symmetrical division in mitosis?
Generates 2 neural stem cells by dividing vertically
What happens if there is an asymmetrical division in mitosis?
Generate a neuroblast & progenitor cell by dividing horizontally
What is a neuroblast?
Postmiotic, immature nerve cell that will differentiate into a neuron
What factors determine fate of migrating neuron?
Age of precursor cell
Position in ventricular zone
Environment at time of division
What are the 3 stages to the growth cone?
Pathway selection
Target selection
Address selection
Give an example of a pathway selection
Retinal ganglion cell reaching correct thalamic location
Give an example of a target selection
Selective the appropriate thalamic nucleus
Give an example of a chemoattractant
Netrin
Give an example of a chemorepellent
Slit
Where is netrin secreted from and what happens after it is secreted?
By cells in ventral midline of spinal cord
Axons with appropriate netrin receptors are attracted to region of highest netrin concentration
Where is slit secreted from and what happens after it is secreted?
By midline cells.
Axons expressing the protein robs grow away from the region of highest slit concentration
Give an example of a neurotrophic factor
Nerve growth factor
What is synapse elimination?
Synaptic capacity
Selective loss of acetylcholine receptors
Muscle fibre initially receives input from several alpha motor neurons but during development all but one input are lost.
Postsynaptic acetylcholine loss precede withdrawal of the axon branch
What are the intrinsic cellular & molecular mechanisms involved in the first steps of conducting brain circuitry?
Establishment of distinct brain regions Neurogenesis Major axon tracts Guidance of growing axons to appropriate targets Initiation of synaptogenesis
When is the activity mediated influence most consequential on the developing brain?
During temporal windows (critical periods)
What are the critical periods?
Variable time windows for different skills / behaviours
What are the requirements for successful completion of the critical period?
Availability of appropriate influences
Neural capacity to respond to them
What are some hypotheses for why critical periods end?
Less potential axon growth
Synaptic transmission matures, less potential changes here
Constraint cortical activation
How does the visual cortex adapt in the blind?
Starts responding to somatosensory signal
Describe peripheral nerve regeneration
Macrophages clear debris from degenerating peripheral stump
Schwann cells proliferate
Express adhesion molecules on their surface & secrete neurotrophins & other growth-promoting signalling molecules
Parent neuron of regenerating axon expresses gene that restores it to a growth state
Describe central nerve regeneration
Local cellular changes at or near injured sites including degeneration of myelin & other cellular elements
Clearing of debris by microglia
Local production of inhibitory factors by astrocytes, oligodendroglia & microglia
Glial scar formation
What are the barriers to regulation after cortical development?
Less neurogenesis
No migration
No radial glial cells
Neuronal plasticity is restricted
Parenchymal glia don’t generate neurons & become reactive after neurodegeneration
Axon pathfinding molecules may be absent & axon tracts are considerably lengthened in adult
What would happen if neurogenesis could no longer occur in the hippocampus?
New events are limited by set of sparse codes provided by mature granulate cells in dentate gyrus
Dentate gyrus won’t have flexibility to encode new memories well or to interference between memories formed in hippocampus
Why are older memories preserved?
They are presented by older neurons
