12- Embryo 1 Flashcards
Primary axes of CNS
rostro-caudal axis = “Nose to tail” axis
dorso-ventral axis complicated by neural tube
How does neural tube complciate dorso-ventral axis
b/c neural tube takes 80degr turn at cephalic flexure (btwn dien/mesenceph) and forms
portion of CNS above flexure (where dorsal assoc with superior and ventral assoc with inferior)
portion below flexure dorsal is towards the back
3 main planes to view the NS
sagittal
coronal (frontal)
axial (transverse or horizontal)
How is nervous system because segment into rostrocaudal segments
1) developing neural tube enlarges at rostral end –> 3 primary cerebral vesicles (pros, mes, rhomb)
2) primary become segmented into secondary vesicles
3) caudal to myelencephalon is early spinal cord
what does prosencephalon vesicle become
pair of telencephalic vesicle + more caudal diencephalic vesicle
what does mesencephalic vesicle become
mesencephalon (no segmentation further)
what does rhombencephalon become
metencephalon
more caudal myelencephalon
Cerebral vesicles are segments of ___
hollow neural tube
difference btwn what vesicles develop into vs neural tube
vesicles = adult structures of CNS
lumen of neural tube = adult CNS architecture
paired telencephalic vesicles have lumen and become ___
lateral ventricles of cerebrum
lumen of diencephalon becomes ___
3rd ventricle
mesencephalon’s lumen gives rise to ___
cerebral aqueduct
aqueduct of Sylvius
lumen of rhombencephalon (both metencephalon + myelencephalon) give rise to ___
4th ventricle
lumen of developing spinal cord give rise to ___
central canal
Rhombencephalon is comprised of ___ which are morphologically distinct
8 rhombomeres
Early in development, rhombomeres ___ but each one ___
resemble each other in size and # of cells but each one develops differently
What genes expressed in rhombencephalon
these genes expressed in ___ manner meaning
Hox (homeobox genes)
each expressed in combinatorial manner so each has specific set of Hox genes that define each rhombomere
what creates the different combinations of Hox genes
morphogen gradients in rostro-caudal and antero-posterior axis
what does a given combination of Hox genes create?
actives distinct pattern of differentiation by affecting transcription –> thus each rhombomere differentiates differently
motor neurons of ___ arise from rhombencephalon
each motor nerve originate from __
thus ___ is an early step in CN formation
CN 4, 5, 6, 7, 9, 10, 11, 12
originate from single rhombomere or pair of neighboring rhombomeres
Hox gene expression
General scheme of dorsoventral patterning of neural tube into alar and basal plate
DV patterning determined by ____
DV patterning determed by morphogen gradients with differential expression of Hox
1) when neural plate forms neural tube, lateral ectoderm lips brought together on dorsal side
2) thus, BMPs highest on dorsal tube and Shh highest near notochord on ventral tube
3) therefore, regional diff in Hox gene expression –> diff cell pop’n
most important morphogens in DV patterning and secreted from where and where located
BMPs
secreted by lateral ectoderm
located at dorsal tube
Shh
secrete by notochord
located at ventral tube
Neural progenitor cells develop into specific populations based on ___
NT creases to separate dorsal and ventral
Ventral pop’n called __ and develop into __
Dorsal pop’n called __
and develop into __
position along DV axis
Ventral = basal plate = motor neurons
Dorsal = alar plate = sensory neurons
morphogen gradients in DV patterning of the prosencephalon are ___ as those for midbrain and more caudal
Shh concentration therefore highest where?
BMP concentration highest where?
the same!
Shh = ventral tube near notochord
BMP = dorsal tube
