Transcript embryology of BRAIN & SPINE

embryology of BRAIN & SPINE
saRavanan
overview
Dorsal induction
Ventral induction
Neuronal prolif.,diff.&histogenesis
Neuronal migration
Axonal myelination
dorsal induction
Formation of neural plate, notochord, neural
groove, neural fold and neural tube
4 – 7 wks
Primary neurulation
Secondary neurulation
ventral induction
Formation of brain vesicles, telencephalon,
diencephalon, mesencephalon,
metencephalon, myelencephalon
5 – 10 wks
neuronal prolif. , diff. & histogenesis
Germinal matrix formation, prolif of neurons &
differentiation, choroid plexus formation and
CSF formation
2 – 5 months and after birth
neuronal migration
from ventricular, subventricular layers around
primitive brain vesicles
to supf cortex,deep nuc of cerebrum &
cerebellum
3,4,5 months
formation of corpus callosum, commissures,
interhemispheric neuronal migrations
axonal myelination
Starts at brainstem, cerebellum, thalamus,
internal capsule
Other areas after birth
3wks – 2yrs and into adolescence
2 days
2 cell stage
3 days
4 cell stage
morulation
morula
4 days
embryoblast
blastocele
trophoblast
blastocyst formation
8 days
Amniogenic cells
Amniotic cavity
Ectoderm (columnar)
Endoderm (cubical)
Trophoblastic cells
Yolk sac
bilaminar disc
16 days
Prochordal plate
(cubical->columnar endoderm)
gastrulation
17 days
Primitive streak
(prolif of ectoderm)
gastrulation
19 days
Mesodermal prolif
(intra embryonic)
gastrulation
19 days
Prochordal plate
(cubical->columnar endoderm)
Mesodermal prolif
(intra embryonic)
Primitive streak
(prolif of ectoderm)
gastrulation (trilaminar disc)
20 days
Prochordal plate
Notochordal process
Primitive knot/primitive node/
HENSON’s node
Primitive streak elongates
Cloacal memb
Notochord formation
21-23 days
neural tube formation
Notochord guides NT formation
Ectoderm overlying notochord from prochordal
plate to primitive node
Primary Neurulation- from neural plate, cranial
end to L1,L2
Secondary Neurulation- lower L,S,Co from caudal
cell mass; no neural plate
neural tube formation
Neural groove <Median Hinge Protein>
Elevation&Convergence <DorsoLateral Hinge Protein>
Closure: middle- cranial(25 day)- caudal(27 day)
Neural crest from edge of neural plate to dorsum
of Neural tube
Dysjn. of cutaneous & neural ectoderm
neural tube formation
neural tube formation
somites
Intraemb mesoderm-paraxial,lateral plate,intermed
Paraxial mesoderm segmented to form SOMITES
on either side of neural tube
--dorsolateral Dermatomyotome: skeletal muscle,
dermis
--ventromedial Sclerotome: cartilage, bone,
ligaments of vertebral column
cranial neuropore
somites
caudal neuropore
Neural Tube- CNS (brain & spinal cord)
Neural Crest- PNS & ANS
Somites- skull, vertebra, ligaments, muscle
Notochord- induces
neurectoderm- Neural tube and deriv.
mesenchyme- spinal column, ligaments, muscles
remains nucleus pulposus
neural tube derivatives
neural tube divisions
primitive ventricles
neural tube flexures
neural tube histology
Matrix layer/ependymal/germinal layernerve cells, glial cells & more germinal cells produced
Mantle layerdeveloping nerve cells & glial cells
Marginal layerno nerve cells; reticulum of glial cells into which
developing nerve cells grow
neural tube histology
cells
Neuroblasts (apolar-bipolar- multipolar-dendrites
formation-synapse formation) neurons
Glioblasts/Medulloblasts
astroblastsastrocytes
oligodendroblastsoligodendrocytes
Mesodermal (migrates along with blood vessels)
microglia
myelination
PNS
Schwann cells (from neural crest) invaginates
around axon and forms multiple layers into
which lipids are deposited
CNS
Oligodendrocytes form myelin sheath
myelination
spinal cord
dorsal part grows faster,thicker,forms-
basal lamina- motor in function
alar lamina- sensory in function
divided by sulcus limitans
dorsal nerve roots are formed from neural crest
Recession of spinal cord due to relative differential
growth
spinal cord
recession spinal cord
medulla
From Myelencephalon
Roof plate widens
Sulcus limitans divides
dorsal(lateral) alar laminacaudal bulbopontine extension
olivary nuclei
Sensory nuclei of cranial n of medulla
ventral(medial) basal laminaMotor nuclei of cranial n of medulla
pons
From ventral part of Metencephalon
Cranial bulbopontine extension pontine nuclei
Axons of bulbopontine extension Middle
cerebellar peduncle
Alar and basal lamina cranial n nuclei
Fibres from cortex corticospinal, corticopontine&
corticobulbar tracts
Lateralpart of alar lamina rhombic lip
(cerebellum)
midbrain
From mesencephalon
Dorsal or alar lamina
oculomotor n nuc
trochlear n nuc
Edinger Westphal nuc
Ventral or basal lamina
cells of colliculi
red nucleus
substantia nigra
Descending fibres form crus cerebri/basis pedunculi
cerebellum
From dorsolateral part of alar lamina of Metencephalon
Cells migrate from mantle -marginal layer Cortex
Cells that do not migrate dentate, emboliform,
globose& fastigial nuclei
Supr cerebellar peduncle- axons out of dentate nucleus
Middle- axons from pontine nuclei into cerebellum
Inferior- axons from spinal cord & medulla
cerebrum
from two telencephalic vesicles of
prosencephalon
Forms together with Corpus striatum
Grows upward, forward, backwards..
Encloses lateral ventricles within
Medial wall invaginates – choroid fissure
Fold of pia extends in-- telachoroidea
Tuft of capillaries enter– choroid plexus
thalamus&hypothalamus
From diencephalon
Two grooves—
epithalamic sulcus
hypothalamic sulcus
Forms three regions—
epithalamus(habenular nuc&pineal body)
thalamus
hypothalamus
neural crest derivatives
neural crest derivatives
Neurons of spinal postr nerve root ganglion
Neurons of sensory ganglia of V,VII,VIII.IX,X
Neurons of Sympathetic ganglia
Schwann cells of all peripheral nerves
Cells of adrenal medulla
Chromaffn tissue
Melanoblasts of skin
ANS
Sympathetic
preganglionic– mantle region of T1 – L2,3
postganglionic– neural crest
Parasympathtic
preganglionic–
cranial- GVE brainstem- EW nuc, salivary,
lacrimatory, dorsal nuc of X
sacral- mantle layer of sacral spinal cord
postganglionic-same regions
mesenchyme derivatives
skull
-viscerocranium(from neural crest) bones of face
-neurocranium(from mesoderm of occipital somites)
--membranous part vault of skull with flat bones separated
by sutures
--cartilaginous part base of skull wth many ossific centres
Postr fontanelle closes by 2 months
Antr fontanelle closes by 2 years
Defects:
anencephaly, scaphocephaly, plagiocephaly,microcephaly,
mandibulo facial dysostosis, cong hydrocephalus
vertebra
From sclerotomes of somites
Sclerotome- 3 parts; cranial, middle, caudal
Vertebra- fusion of caudal part of upper & cranial part
of lower sclerotome, so intersegmental
IVD- from middle part, so segmental
Sequential steps of membrane formation,
chondrification& ossification
defects: absent, additional, bifida, hemivertebra,
fusion(klippelfeil,sacralisation,occipitalisation,
lumbarisation), listhesis, sacrococc teratoma,
diastematomylia, scoliosis
vertebra
notochord
somites
cranial part
middle part
caudal part
IVD
vertebra
Nucleus
pulposus
vessels
ICA- third primitive aortic arch A
ACA- primitive olfactory A
A Com- joining of two primitive olfactory A
MCA- arises from ICA
ECA- outgrowth of extension of primitive third aortic
arch
Basilar A- primitive basilar A
PCA- fusion of many primitive antr arch A as extension
of ICA,then shifts to Basilar A
meninges
Primitive Meninx
from loose mesenchyme surrounding the
developing neural tube
factors in neurodevelopment
Growth Cone
Raman Y Cajal, 1890
expanded end of growing axon which is active,
exploring, develops growing along suitable surface to
form dendrites
factors in neurodevelopment
Growth factors (neurotrophins)
NGF,
BDNF,
NT-3, NT-4, NT-5,
ciliary NTF,
FGF
factors in neurodevelopment
Receptors
P75 NTF
Trk s
factors in neurodevelopment
Inducers
Noggin
Chordin
Follistatin (inhibits BMP )
(Bone Morphogenetic Protein inhibits Neural Tube formation)
factors in neurodevelopment
Genes
Hox a,b,c,d
Pax
Dlx
Emx
Otx
defects in neurodevelopment
Dorsal induction- anencephaly, cephaloceles, Chiaris, spinal
dysraphisms,caudal regression synd, tethered cord
Ventral induction- holoprosencephalies, septoopticdysplasia,
Dandy Walker, Joubert’s, facial anamolies
Neur prolif, Diff, Histog- micro,megalocephaly, neurocut. synd,
aqueductal stenosis, arachnoid cysts
Neur migration- schizencephaly, lissencephaly, heterotopias,
callosal agenesis, pachy/polymicrogyria
defects in neurodevelopment
contd..
Myelination- dysmyelinating diseases
Acquired(degen,toxic,inflmm)- hydranencephaly,
hemiatrophy, multicystic encephalomalacia, periventric
leukomalacia
Chromosomal/Genetic- structural deformities to mental
retardation to death
references
Human Embryology: Inderbir Singh & G.P.Pal,
7thEd
Gray’s anatomy- the anatmical basis of clinical
practice: Henry Gray, 39th Ed
Brain development and congenital
malformations: Anne G.Osborn & Richard S.
Boyer
Atlas of neuroradiological embryology,anatomy
& variations: J.Randy Jinkins
thank U..