embryology of BRAIN & SPINE

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->columnar 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->columnar endoderm) Mesodermal prolif (intra embryonic) Primitive streak (prolif of ectoderm)

15. Notochord formation 20 days Prochordal plate Notochordal process Primitive knot/primitive node/ HENSON’s 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 <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

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oligodendrocytes 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 Sulcuslimitansdivides 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 fromtwo 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. thalamus&hypothalamus From diencephalon Two grooves— epithalamic sulcus hypothalamic sulcus Forms three regions— epithalamus(habenular nuc&pineal 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,microcephaly, mandibulo facial dysostosis, cong hydrocephalus

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,occipitalisation, 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