embryology of BRAIN

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embryology of BRAIN SPINE

• saRavanan

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overview

• Dorsal induction
• Ventral induction
• Neuronal prolif.,diff.histogenesis
• Neuronal migration
• Axonal myelination

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dorsal induction

• Formation of neural plate, notochord, neural
  groove, neural fold and neural tube
• 4 7 wks
• Primary neurulation
• Secondary neurulation

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ventral induction

• Formation of brain vesicles, telencephalon,
  diencephalon, mesencephalon, metencephalon,
  myelencephalon
• 5 10 wks

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neuronal prolif. , diff. histogenesis

• Germinal matrix formation, prolif of neurons
  differentiation, choroid plexus formation and CSF
  formation
• 2 5 months and after birth

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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

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axonal myelination

• Starts at brainstem, cerebellum, thalamus,
  internal capsule
• Other areas after birth
• 3wks 2yrs and into adolescence

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morulation
2 days
3 days
2 cell stage
4 cell stage
morula
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blastocyst formation
4 days
embryoblast
blastocele
trophoblast
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bilaminar disc
8 days
Amniogenic cells
Amniotic cavity
Ectoderm (columnar)
Endoderm (cubical)
Trophoblastic cells
Yolk sac
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gastrulation
16 days
Prochordal plate (cubical-gtcolumnar endoderm)
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gastrulation
17 days
Primitive streak (prolif of ectoderm)
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gastrulation
19 days
Mesodermal prolif (intra embryonic)
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gastrulation (trilaminar disc)
19 days
Prochordal plate (cubical-gtcolumnar endoderm)
Mesodermal prolif (intra embryonic)
Primitive streak (prolif of ectoderm)
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Notochord formation
20 days
Prochordal plate
Notochordal process
Primitive knot/primitive node/ HENSONs node
Primitive streak elongates
Cloacal memb
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neural tube formation
21-23 days

• 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
• 
  
  
  
  
  

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neural tube formation

• Neural groove ltMedian Hinge Proteingt
• ElevationConvergence ltDorsoLateral Hinge
  Proteingt
• 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

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neural tube formation
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neural tube formation
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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

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cranial neuropore
somites
caudal neuropore
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• 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

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neural tube derivatives
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neural tube divisions
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primitive ventricles
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neural tube flexures
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neural tube histology

• Matrix layer/ependymal/germinal layer-
• nerve cells, glial cells more germinal cells
  produced
• Mantle layer-
• developing nerve cells glial cells
• Marginal layer-
• no nerve cells reticulum of glial cells into
  which developing nerve cells grow

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neural tube histology
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cells

• Neuroblasts (apolar-bipolar- multipolar-dendrites
  formation-synapse formation) ?neurons
• Glioblasts/Medulloblasts
• 
  astroblasts?astrocytes
• oligodendroblasts?oligodendroc
  ytes
• Mesodermal (migrates along with blood vessels)
• 
  ?microglia

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myelination

• PNS
• Schwann cells (from neural crest) invaginates
  around axon and forms multiple layers into which
  lipids are deposited
• CNS
• Oligodendrocytes form myelin sheath

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myelination
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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

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spinal cord
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recession spinal cord
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medulla

• From Myelencephalon
• Roof plate widens
• Sulcus limitans divides
• dorsal(lateral) alar lamina-
• caudal bulbopontine extension
• olivary nuclei
• Sensory nuclei of cranial n of
  medulla
• ventral(medial) basal lamina-
• Motor nuclei of cranial n of
  medulla

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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)

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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

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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

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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

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thalamushypothalamus

• From diencephalon
• Two grooves
• epithalamic sulcus
• hypothalamic sulcus
• Forms three regions
• epithalamus(habenular nucpineal body)
• thalamus
• hypothalamus

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neural crest derivatives
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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

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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

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mesenchyme derivatives
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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,microce
  phaly, mandibulo facial dysostosis, cong
  hydrocephalus

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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,occ
  ipitalisation, lumbarisation), listhesis,
  sacrococc teratoma, diastematomylia, scoliosis

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vertebra
notochord
cranial part
middle part
IVD
caudal part
vertebra
somites
Nucleus pulposus
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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

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meninges

• Primitive Meninx
• from loose mesenchyme surrounding the developing
  neural tube

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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

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factors in neurodevelopment

• Growth factors (neurotrophins)
• NGF,
• BDNF,
• NT-3, NT-4, NT-5,
• ciliary NTF,
• FGF

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factors in neurodevelopment

• Receptors
• P75 NTF
• Trk s

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factors in neurodevelopment

• Inducers
• Noggin
• Chordin
• Follistatin (inhibits BMP )
• (Bone Morphogenetic Protein inhibits Neural Tube
  formation)

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factors in neurodevelopment

• Genes
• Hox a,b,c,d
• Pax
• Dlx
• Emx
• Otx

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defects in neurodevelopment

• Dorsal induction- anencephaly, cephaloceles,
  Chiaris, spinal dysraphisms,caudal regression
  synd, tethered cord
• Ventral induction- holoprosencephalies,
  septoopticdysplasia, Dandy Walker, Jouberts,
  facial anamolies
• Neur prolif, Diff, Histog- micro,megalocephaly,
  neurocut. synd, aqueductal stenosis, arachnoid
  cysts
• Neur migration- schizencephaly, lissencephaly,
  heterotopias, callosal agenesis,
  pachy/polymicrogyria

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defects in neurodevelopment
contd..
Myelination- dysmyelinating diseases Acquired(de
gen,toxic,inflmm)- hydranencephaly, hemiatrophy,
multicystic encephalomalacia, periventric
leukomalacia Chromosomal/Genetic- structural
deformities to mental retardation to death
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references

• Human Embryology Inderbir Singh G.P.Pal, 7thEd
• Grays 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

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thank
U..