Neuronal Development Flashcards
What percentage of synapses are eliminated after development?
~50%
If the human brain were a computer, what would its storage capacity be?
1000TB
What is neurogenesis?
Neurones are born
What is migration?
Neurones find their place and build
What is differentiation?
Determination of cell fate
What is target innervation?
Address selection
What is synapse formation?
Creation of connections
What occurs first in neuronal development?
Gastrulation
What is gastrulation?
Embryo transforms into a single layer of epithelial cells
Where and when do the primitive streak and notochord form?
At the midline during gastrulation
What are the three primitive cell layers that develop during gastrulation?
Endoderm, mesoderm, ectoderm
How does the neural plate come about?
Ectoderm thickens after gastrulation
Which epithelium gives rise to the entire nervous system?
Neural plate
How is the neural groove invagination formed?
Uneven rates of cell division at the neural plate
How is the neural tube formed?
Neural groove joins together
hen do neural crest cells develop?
As the neural tube is formed
What does the neural tube eventually become?
Fluid-filled cerebral ventricles of the brain and spinal cord
Where does the roofplate form?
Where the neural tube closes
Where does the floorplate form?
Above the notochord
Which are the three transient structures during neural development?
Roofplate, floorplate, notochord
When do the brain subdivisions become discernible?
After the neural tube and crest have developed
What are the three brain subdivisions?
Prosencephalon, mesencephalon, rhombencephalon
What is the proencephalon?
Forebrain
What is the mesencephalon?
Midbrain
What is the rhombencephalon?
Hindbrain
What do neural stem cells in the neural tube replicate into by mitosis?
More stem cells or neuroblasts
What are neuroblasts the precursor of?
Neurones
What are neuroblasts the precursor of?
Neurones
What are neuroblasts the precursor of?
Neurones
When do the ventricular and marginal zones form?
During neurogenesis
How do neurones find their destination during migration?
Move along surface of radial glia acting as guidelines
What occurs once neurones have migrated?
Differentiation to form different cell populations
Which end is the brain formed at?
Anterior
What forms the spinal cord?
Neural tube near somites
What forms the major components of the PNS?
Neural crest separating from the neural tube
What becomes CSF ventricles?
Lumen of neural tube
What in the brain distinguishes humans from other animals?
Size of cortex / frontal lobe
What do morphogens do?
Instruct a high degree of patterning in the neural tube
What patterning occurs along the length of the neural tube?
Anterior/posterior (rostral/caudal)
What patterning occurs in the cross-section of the neural tube?
Dorsal/ventral
What determines the ultimate fate of a neurone?
Where and when it was produced
What is an example of morphogen gradients driving differentiation?
FGF/BMPs influencing transcription factors for anterior/posterior differentiation
What are Hox genes?
Family of TFs that establish segmentation along the anterior/posterior axis
What is synophthalmia?
Cyclopia - Development of one large eye
How do cyclops cows come about?
Mother eats a certain plant, Sonic hedgehog inhibition leads to loss of ventral identity
What are the neural precursor cells in the neural tube?
Neuroepithelium / neuroepithelial progenitor cells
What do radial glia connect in the developing cortex?
Ventricular and pial surfaces
What is the innermost layer of the neural tube?
Ventricular zone
How are transit amplifying cells generated?
Asymmetrical division of cells in the ventricular zone
What is the outermost layer of the neural tube?
Pial surface
What forms the marginal zone of the cortex?
Neuroblasts migrating to the pial surface
In which direction is the cortex built?
Inside out, with newer neuroblasts migrating past their older cousins
How can the columnar organisation of the cortex be used to reveal the birthdate of a neurone?
Correlates to location like a tree ring
Which type of cortical neural cell has a different origin to others?
Interneurones
Where are cortical interneurones born?
Ganglionic eminences
Where do glial cells originate?
Neuroepithelium
What can glioblasts become?
Ependymal cells, astrocytes or oligodendrocytes
How does a glioblast differentiate into an ependymal cell?
Remains attached to the lumen
What is the function of ependymal cells?
Production of CSF
How does a glioblast differentiate into an astrocyte or oligodendrocyte?
Moves to marginal layer
What is the function of astrocytes?
Maintenance and repair
What is the function of oligodendrocytes?
Myelination
What are the two steps of target innervation?
Polarisation and fasciculation
What occurs in the polarisation stage of target innervation?
Cell body establishes axons and dendrites
Which part of the neurone moves during polarisation (target innervation)?
The growing axon - Cell body stays put
How do growing processes navigate between stepping stones during polarisation (target innervation)?
Using cues and signals
What occurs in the fasciculation stage of target innervation?
Axons piggy-back along existing neurones
How do pioneering axons navigate during fasciculation (target innervation)?
Piggy-back along other tissue types
What is the growth cone?
Tip of axon that recognises guidance signals and cues in target innervation
What are the properties of non-diffusible guidance signals?
Short-range, substrate-derived, present in ECM or target cells
What are the properties of diffusible guidance signals?
Long-range, act as gradients
What are cadherins and ephrins examples of?
Non-diffusible guidance signals for target innervation
What are netrin and semaphorins examples of?
Diffusible guidance signals for target innervation
What is the structure of a growth cone?
Hand-like with surface receptors
What are the types of growth cone?
Filopodia and lamellipodia
What does the commissural interneurone determine?
Left-right coordination
What is the first attraction experienced by the commissural interneurone during development?
Long-range attraction to the floorplate
What happens after the commissural interneurone reaches the floorplate?
Growth cone switches sensitivity from attractive to repulsive to leave the area so it crosses the midline once
Why don’t motor neurones cross the midline?
Midline always repulsive, they don’t need to cross
How does the growth cone move towards or away from guidance cues?
Actin cytoskeletal changes
Once the direction of an axon is determined, how is it laid down in the desired location?
Microtubular cytoskeletal changes
What do adhesion molecules do?
Stabilise formed connections between neurones
What do presynaptic neurexins do?
Organise the synaptic vesicle docking zone
What do postsynaptic neuroligins do?
Recruit postsynaptic receptors
How is the final pattern of neural contacts determined?
Neurotrophins and electrical activity
Why are synapses and cells made in excess and then abandoned as needed?
To ensure robust, functionally required circuits
What happens when a limb is removed from a foetus?
Reduced motor and sensory neurones in the spinal cord
What happens when a limb is grafted onto a foetus?
Increased motor pool where the extra limb is grafted
How does the target regulate neurone circuits?
Continued release of trophic factors, and activity
