L5 - Origin and patterning of the nervous system

Question 1

central nervous system

Answer 1

processing of sensory info an coordination of motor output

central
cerebrum
cerebellum
bainstem
spinal cord
root ganglia -

vs peripheral
paraxial mesoderm/ganglia

Question 2

vertebrae brain

Answer 2

neurones
glia cells
astrocytes
axons myelinated by oligodendrocytes

Question 3

triple origin of the nervous system

Answer 3

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

Question 4

identification/grafting of the organiser

Answer 4

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

Question 5

BMP signalling

Answer 5

working on mesoderm (ventral fate) and ectoderm (epidermal fate) for patterning

role of the inhibitors i.e. noggin is the opposite

Question 6

formation of the neural tube

primary neurulation

Answer 6

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

2. 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

Question 7

when neurulation goes wrong

Answer 7

defects in neural tube closure lead to clinical problems
1.spina bifida - along spinal cord - can be recognised in a scan and resolved surgically

2. exencephaly - in brain - feotus will not survive

Question 8

neural crest cells origin

Answer 8

originates at border between epidermal ectoderm and neuro-ectoderm

part of root plate
leave epithelium into periphery

Question 9

neural crest migration

Answer 9

2 streams

1. cells can form melanocytes or skeletal tissue follow dorsolateral path
2. cells with neural fate follow ventromedial path through the anterior half of the somites - sclerotome

Question 10

neural crest fate

Answer 10

depending on position of origin

head = cranial ganglia
trnk = dorsal root ganglia , enteric ganglia, autonomic nervous sys, schwann cells

Question 11

when neural crest formation goes wrong

Answer 11

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

Question 12

placodes

Answer 12

contribute to 
sense organs 
olfactory epithelium 
lens
otic epithelium
more later
cranial ganglia = can also originate from neural crest

Question 13

neural tube patterning

Answer 13

dorso-ventral = sensory-motor

rostrocaudal = forebrain-midbrain-hindbrain-spinal cord

Question 14

patterning of the ventral spinal cord

Answer 14

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

Question 15

neuronal fate in the spinal cord

Answer 15

patterning by floor plate and roof plate

specific expression of transcription factors in progenitors

distinct expression of homeobox genes in differentiating neurones

Question 16

when ventral signalling goes wrong

Answer 16

shh signalling from prechordal plate is required to split eye field and fore brain

defect = brain -holoprosencephaly and cyclopia

Question 17

shared brain structure in vertebrates

Answer 17

forebrain
midbrain
hindbrain

telencephalon
diencephalon
mesencephalon
cerebellum
pons
medulla

Question 18

anterior posterior CNS organisation in vertebrates

Answer 18

3 vesicles later 5 vesicles

vesicles
bulges correspond to the main subdivisions: the forebrain
midbrain
hindbrain

Question 19

Anterior CNS patterning

Answer 19

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

Question 20

brain organisation

Answer 20

dorsoventral organisation

• roof plate rhombencephalon:
• alar plate
• basalplate
• floor plate = xetends throughout brain

along anteroposterior axis = brain compartmentalised

Question 21

embryonic hindbrain

Answer 21

rhombomeres: along rostrocaudal axis constrictions divide hindbrain into swellings

cranial nerves emerge from hindbrain including those that supply the pharyngeal branchial arch muscles

Question 22

crainial ganglia

Answer 22

located next to the hindbrain
their axons enter the hindbrain in the even numbered rhombomeres

12 crainial neres
mainly associated w hindbrain n rhombomeres

Question 23

anteriorly expressed hox genes

Answer 23

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

Question 24

formation of the nervous system

Answer 24

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