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embryology of BRAIN

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embryology of BRAIN & SPINE saRavanan recession spinal cord medulla From Myelencephalon Roof plate widens Sulcus limitans divides dorsal(lateral) alar lamina ... – PowerPoint PPT presentation

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Title: embryology of BRAIN


1
embryology of BRAIN SPINE
  • saRavanan

2
overview
  • Dorsal induction
  • Ventral induction
  • Neuronal prolif.,diff.histogenesis
  • Neuronal migration
  • Axonal myelination

3
dorsal induction
  • Formation of neural plate, notochord, neural
    groove, neural fold and neural tube
  • 4 7 wks
  • Primary neurulation
  • Secondary neurulation

4
ventral induction
  • Formation of brain vesicles, telencephalon,
    diencephalon, mesencephalon, metencephalon,
    myelencephalon
  • 5 10 wks

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

6
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

7
axonal myelination
  • Starts at brainstem, cerebellum, thalamus,
    internal capsule
  • Other areas after birth
  • 3wks 2yrs and into adolescence

8
morulation
2 days
3 days
2 cell stage
4 cell stage
morula
9
blastocyst formation
4 days
embryoblast
blastocele
trophoblast
10
bilaminar disc
8 days
Amniogenic cells
Amniotic cavity
Ectoderm (columnar)
Endoderm (cubical)
Trophoblastic cells
Yolk sac
11
gastrulation
16 days
Prochordal plate (cubical-gtcolumnar endoderm)
12
gastrulation
17 days
Primitive streak (prolif of ectoderm)
13
gastrulation
19 days
Mesodermal prolif (intra embryonic)
14
gastrulation (trilaminar disc)
19 days
Prochordal plate (cubical-gtcolumnar endoderm)
Mesodermal prolif (intra embryonic)
Primitive streak (prolif of ectoderm)
15
Notochord formation
20 days
Prochordal plate
Notochordal process
Primitive knot/primitive node/ HENSONs node
Primitive streak elongates
Cloacal memb
16
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






17
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

18
neural tube formation
19
neural tube formation
20
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

21
cranial neuropore
somites
caudal neuropore
22
  • 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

23
neural tube derivatives
24
neural tube divisions
25
primitive ventricles
26
neural tube flexures
27
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

28
neural tube histology
29
cells
  • Neuroblasts (apolar-bipolar- multipolar-dendrites
    formation-synapse formation) ?neurons
  • Glioblasts/Medulloblasts

  • astroblasts?astrocytes
  • oligodendroblasts?oligodendroc
    ytes
  • Mesodermal (migrates along with blood vessels)

  • ?microglia

30
myelination
  • PNS
  • Schwann cells (from neural crest) invaginates
    around axon and forms multiple layers into which
    lipids are deposited
  • CNS
  • Oligodendrocytes form myelin sheath

31
myelination
32
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

33
spinal cord
34
recession spinal cord
35
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

36
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)

37
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

38
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

39
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

40
thalamushypothalamus
  • From diencephalon
  • Two grooves
  • epithalamic sulcus
  • hypothalamic sulcus
  • Forms three regions
  • epithalamus(habenular nucpineal body)
  • thalamus
  • hypothalamus

41
neural crest derivatives
42
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

43
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

44
mesenchyme derivatives
45
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

46
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47
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

48
vertebra
notochord
cranial part
middle part
IVD
caudal part
vertebra
somites
Nucleus pulposus
49
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

50
meninges
  • Primitive Meninx
  • from loose mesenchyme surrounding the developing
    neural tube

51
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

52
factors in neurodevelopment
  • Growth factors (neurotrophins)
  • NGF,
  • BDNF,
  • NT-3, NT-4, NT-5,
  • ciliary NTF,
  • FGF

53
factors in neurodevelopment
  • Receptors
  • P75 NTF
  • Trk s

54
factors in neurodevelopment
  • Inducers
  • Noggin
  • Chordin
  • Follistatin (inhibits BMP )
  • (Bone Morphogenetic Protein inhibits Neural Tube
    formation)

55
factors in neurodevelopment
  • Genes
  • Hox a,b,c,d
  • Pax
  • Dlx
  • Emx
  • Otx

56
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

57
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
58
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

59
thank
U..
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