brain development

Question 1

notochord how is it formed

Answer 1

form aggregation of the mesoderm
which invagenates and extends inwards
from the primitive pit

Question 2

what happens on day 18

Answer 2

notochord forms via invagenation of the mesoderm

Question 3

what happens of day 20

Answer 3

neural plates begin to fold in the mid line
forming the neural grooves
and neural plates at the bottom differentiate forming the floorplate

Question 4

what happens on day 22

Answer 4

neural plates meet forming neural tubes
mesoderm thickens and subdivides
into structures called somites

Question 5

what is a somite

Answer 5

precursor of axial musculature and skeleton

Question 6

what happens on day 24

Answer 6

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

Question 7

neural precursors can give rise to

Answer 7

neurons
astrocytes
oligodendroglia

Question 8

what does the floorplate do

Answer 8

provides specific molecular signals to specify the neuroblast cells
position at the ventral midline defines dorsoventral polarity of the neural tubes

Question 9

what happens to the neural crest cells

Answer 9

migrate away through loosely packed mesenchymal cells that fill the space between the neural tube, embryonic epidermis and somites

Question 10

what happens to subsets of neural crest

Answer 10

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

Question 11

what happens on day 23

Answer 11

neural tube epithlia produce neurons and glia
via progenitor cells
neuroblasts move away from lumen to form outer mantle layer

Question 12

what happens after day 23

Answer 12

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

Question 13

how does progenitor cells know which cell to become

Answer 13

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)

Question 14

what are the induction signal pathways

Answer 14

wnt signalling
sonic hedgehog
fibroblast growth factor
bone morphogentic protein

Question 15

mutation is induction pathways give

Answer 15

wnt = autisum
sonic = medullablastoma

Question 16

once born how does the neuron get to its target

Answer 16

signals released continuously sent to cells
signals recieved by growth cones
neurons will send out processes to their target, by forming synapses

Question 17

what is fasciculation

Answer 17

pioneers get to target, while other cells piggy back the initial process laid out

Question 18

on day 24
what sends inductive signals
to where
and what does it cause

Answer 18

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

Question 19

what does the floorplate give rise too

Answer 19

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

Question 20

what happens on day 23
differentiation
and migration

Answer 20

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