Plasticity and regeneration Flashcards
Inducing factors that determines gene expression
Signalling molecules from other cells, either:
- Diffusible, over long range
- On cell surface, locally
Competence in gene expression
The ability for cell to respond to inducing factors
Depends on:
- Set of receptors on cell
- Transduction molecules
- Transcription factors made by the cell.
Time period for neurogenesis
5th week- 5th month of gestation
Generates almost all neurones for life
Neural stem cells/ precursor cells
Infinitely self-renewing cells of NS
- Located in ventricular zone
Gives rise to range of cell classes within relevant tissue, after terminal division and differentiation
- Inhibitory
- Excitatory
- Glia cells
Neural progenitor cell
Cells of NS incapable of self-renewal
Can only give rise to one class of differentiated progeny cells - E.g oligodendroglial progenitor can only give rise to oligodendrocytes
Protein distribution in precursor neural cells
Notch-1 protein= superior pole
Numb protein= inferior pole
- Both distributed differently in precursor cells of developing neocortex
Vertical cleavage of cell= identical sister cell produced
- equal proportion of proteins
Horizontal cleavage= different sister cells produced
- Neuroblast [Notch-1 end]
- Progenitor cell [Numb end]
Neuroblast
Post-mitotic, immature nerve cell that differentiates into a neurone
- Migrates to other parts of NS
Factors that determine what happens to a migrating neurone
Age of the neural stem cell
Position of ventricular zone
Environment at the time of cell division
Differentiation
Process of when tissues become more specialised during development
- Due to specific spatiotemporal pattern of gene expression
- Inside out development
- Subplate forms scaffolding for many layers
Three steps:
- Pathway selection [select the location]
- Target selection [select the nucleus]
- Address selection [select layer/ position in tissue]
Neuroblast differentiation
Growth cone:
Extension of neurite
Filopodia:
Allows neuroblast to navigate around environemnt
Netrin
Chemoattractant
- Produced in ventral midline of spinal cord
- Promotes growth of axons towards it
Slit
Chemorepellent secreted by midline cells
- Axons turn and extend away from it
- Robo receptor
Contact-mediated attraction and repulsion
Guidance cue for neuronal growth
Attraction
- Axons come across substrate bound ones and extend along their cell surface
Repulsion
- Axons come across substrate bound ones and retract growth cones
Neurotrophic factors
Biomolecules that support the growth, survival, and differentiation of neurons.
Example
- Nerve growth factor
Apoptosis and tropic interactions
Programmed cell death is the result of competition for tropic factors
Allows the production for the correct match of presynaptic to post synaptic neurones.
Synaptic elimination
Method of fine-tuning for neuronal connections [e.g at neuromuscular junction]
- Activity dependant
Synaptic capacity
- At first muscle fibre would receive input from many alpha motor neurones
- Overtime in develop, all but one input is lost
Selective loss of AcH receptors
- Blocking postsynaptic AcHr can stimulate its loss
- Leads to withdrawal of axon branch
Critical period
Temporal window for different skills and behaviours
- Sensorimotor skills
- Language acquisition etc
Factors that determine its successful completion:
1. The availability of appropriate influences
- Neural capacity to respond to those influences
Visual perception and sensory experience
Sensory experience is required for visual perception.
Study with ocular dominance columns by Hubel and Wiesel showed:
- 3-6 days monocular deprivation [early after birth] in a baby animal led to ipsilateral vision
- Does not occur in adult animals
Visual deprivation + ocular dominance
Monocular deprivation in critical period led to alternating ocular dominance columns becoming unequal
- Deprived eye column shrinks
- Non-deprived eye column thickens
Hebbian modifications during development
Process that strengthens synapses.
At first inputs fire out of sync into a cell
- Loses its synapses during developing [out of sync]
Inputs in sync undergo Hebbian modification to become more effective
Plasticity in adult cerebral cortex
Functional changes in part of a tissue occur in relation to motor and sensory experience
Example:
- Amputation of the third digit saw cortex responding to digit 3, merged to respond to digit 3 and 4/
Peripheral nerve regeneration
- Macrophages remove myelin debris from injured peripheral nerve.
- Growth related genes are expressed in soma which stimulates production of:
- Axon growth promoting signals
- Neutrophins - Proliferating Schwann cells promote axon regeneration
Central nerve regeneration
- Microglia clears myelin debris from damaged axon.
- Astrocytes, oligodendrocytes and microglia locally produce inhibitory factors
- Glial scar forms
Adult neurogenesis
Only occurs:
- subventricular zone–> olfactory bulb
- Hippocampus
