L5 - Origin and patterning of the nervous system Flashcards
central nervous system
processing of sensory info an coordination of motor output
central cerebrum cerebellum bainstem spinal cord root ganglia -
vs peripheral
paraxial mesoderm/ganglia
vertebrae brain
neurones
glia cells
astrocytes
axons myelinated by oligodendrocytes
triple origin of the nervous system
derivative of the ectoderm
neurones and glia cells have 3 sources
neural plate = motor neurones and retina
neural crest = crainial bone pigment cells + connective tissue
placodes = lens (not retina) + inner ear
identification/grafting of the organiser
working with newts
take dorsal blastopore lip - region that gives rise to notochord
the area through which gastrulation occurs - node in humans
conc=
transplanting a particular region of the early embryo dorsal blastopore lip on the ventral side induces additional embryo
dorsal blastopore lip sends a instruction signal
BMP signalling
working on mesoderm (ventral fate) and ectoderm (epidermal fate) for patterning
role of the inhibitors i.e. noggin is the opposite
formation of the neural tube
primary neurulation
neural induction
fgf signalling and bmp inhibition co operate to induce neural fate
bmp inhibitors secreted by organiser = allow neural development
bmp signalling suppresses neural development = epidermis
results = neural plate is formed around the midline along the anteroposterior or rostercaudal axis
- neurulation
the neural plate folds up to form the neural folds an eventually the neural tube
dertermines the dorsobventral axis of the neural plate
midline becomes floorplate - ventral
lateral edges fuse become root plate - dorsal
when they fuse the neural tube detaches from ectoderm
ectoderm forms. layer ontop
neural canal - filled with cerebrospinal fluid
linked to neurulation is the formation of the neural crest
in the tail instead = secondary neurulation
condensation and epithelialisation around central lumen
when neurulation goes wrong
defects in neural tube closure lead to clinical problems
1.spina bifida - along spinal cord - can be recognised in a scan and resolved surgically
- exencephaly - in brain - feotus will not survive
neural crest cells origin
originates at border between epidermal ectoderm and neuro-ectoderm
part of root plate
leave epithelium into periphery
neural crest migration
2 streams
- cells can form melanocytes or skeletal tissue follow dorsolateral path
- cells with neural fate follow ventromedial path through the anterior half of the somites - sclerotome
neural crest fate
depending on position of origin
head = cranial ganglia trnk = dorsal root ganglia , enteric ganglia, autonomic nervous sys, schwann cells
when neural crest formation goes wrong
Pax3 expressed in orsal neural tube and neural crest
mutation in humans = waardenburg syndrome
mainly neural crest defects but also high risk of spina bifida
placodes
contribute to sense organs olfactory epithelium lens otic epithelium more later cranial ganglia = can also originate from neural crest
neural tube patterning
dorso-ventral = sensory-motor
rostrocaudal = forebrain-midbrain-hindbrain-spinal cord
patterning of the ventral spinal cord
Shh is expressed by notocord to induce floor plate inside neural tube now diffusing inside neural tube forms conc gradient
cells along neural tube exposed to diff conc of Shh
cells right next to to the floor plate are exosed to high conc for longer periods than those more ventrally
neuronal fate in the spinal cord
patterning by floor plate and roof plate
specific expression of transcription factors in progenitors
distinct expression of homeobox genes in differentiating neurones
when ventral signalling goes wrong
shh signalling from prechordal plate is required to split eye field and fore brain
defect = brain -holoprosencephaly and cyclopia
shared brain structure in vertebrates
forebrain
midbrain
hindbrain
telencephalon diencephalon mesencephalon cerebellum pons medulla
anterior posterior CNS organisation in vertebrates
3 vesicles later 5 vesicles
vesicles
bulges correspond to the main subdivisions: the forebrain
midbrain
hindbrain
Anterior CNS patterning
EARLY:
Shh is expressed in the notochord and in the floor plate throughout
ventralising signal along the whole axis
FGF 8 expressed in 2 distinct places
anterior neural ridge
and isthmus mindbrain hindbrain border
imprtant for inducing telencephalon
mes and anterior rhombencephalon
grafting of ectopic isthmus or fgf8 into diencephalon induces mirror image duplication of midbrain
if you leave the embryo for longer
LATER:
additional signalling centres refine the pattern
Shh patterns the diencephelon
brain organisation
dorsoventral organisation
- roof plate rhombencephalon:
- alar plate
- basalplate
- floor plate = xetends throughout brain
along anteroposterior axis = brain compartmentalised
embryonic hindbrain
rhombomeres: along rostrocaudal axis constrictions divide hindbrain into swellings
cranial nerves emerge from hindbrain including those that supply the pharyngeal branchial arch muscles
crainial ganglia
located next to the hindbrain
their axons enter the hindbrain in the even numbered rhombomeres
12 crainial neres
mainly associated w hindbrain n rhombomeres
anteriorly expressed hox genes
hox genes 1-4 expressed in rhombomere specific patterns in the hindbrain
combinatorial expression of hox genes provides unique rcodesfor the individual rhombomeres
hoxb1 expressed in rhombomere4
loss of function or ectopic expression so gain of function experiments alter the morphology of the hindbrain
formation of the nervous system
neurones and glia are derived from the ectoderm
the cna is formd from the neural tube
the pns is formed from neural crest and placodes
neural induction is a function of the organiser
BMP inhibition allows neruectodermal fate
patterning along the anterior posterior and dorsal ventral axes establishes positional identity and allows the generation of the different neuronal cell identities
localised signalling
regionalised expression of transcription factors
