brain development Flashcards
notochord how is it formed
form aggregation of the mesoderm
which invagenates and extends inwards
from the primitive pit
what happens on day 18
notochord forms via invagenation of the mesoderm
what happens of day 20
neural plates begin to fold in the mid line
forming the neural grooves
and neural plates at the bottom differentiate forming the floorplate
what happens on day 22
neural plates meet forming neural tubes
mesoderm thickens and subdivides
into structures called somites
what is a somite
precursor of axial musculature and skeleton
what happens on day 24
neural tubes become spinal cord
neural crest gives rise to sensory and autonomic ganglia
anterior ends of the neural plate grow together at the midline and continues to expand, eventually giving rise to the brain
neural precursors can give rise to
neurons
astrocytes
oligodendroglia
what does the floorplate do
provides specific molecular signals to specify the neuroblast cells
position at the ventral midline defines dorsoventral polarity of the neural tubes
what happens to the neural crest cells
migrate away through loosely packed mesenchymal cells that fill the space between the neural tube, embryonic epidermis and somites
what happens to subsets of neural crest
they follow a specific pathway
exposing them to more inductive signals which influence differentiation
giving rise to neurons, glia of sensory and visceral motor (autonomic) ganglia
what happens on day 23
neural tube epithlia produce neurons and glia
via progenitor cells
neuroblasts move away from lumen to form outer mantle layer
what happens after day 23
neuroglia also produced from neuroepithelia cells
glioblast extend their processes to attach to lumen and outer membrane
overtime, they become ependymal cells
or they move to marginal layer and form astrocytes or oligodendrocytes
how does progenitor cells know which cell to become
signals from notochord and primitive pit
which gives a verity of signal transduction pathways
leading to alterations in the gene expression
(master gene, HOX genes)
what are the induction signal pathways
wnt signalling
sonic hedgehog
fibroblast growth factor
bone morphogentic protein
mutation is induction pathways give
wnt = autisum sonic = medullablastoma
once born how does the neuron get to its target
signals released continuously sent to cells
signals recieved by growth cones
neurons will send out processes to their target, by forming synapses
what is fasciculation
pioneers get to target, while other cells piggy back the initial process laid out
on day 24
what sends inductive signals
to where
and what does it cause
notochord and the primitive pit send induction signals to overlaying ectoderm
causing neuroectoderm cells to differentiate into neural precursor cells (neurulation)
midline ectoderm cells thicken into distinct columnar epithelial called the neural plate
what does the floorplate give rise too
gives rises to spinal and hindbrain motor neurons
precursors further away from ventral midline give rise to sensory relay neurons within the spinal cord and hindbrain
what happens on day 23
differentiation
and migration
differentiation occurs forming neurons becoming grey matter of brain and spinal cord
while the axons of these neurons migrate outwards forming the marginal layer becoming white matter
