Details of central nervous system embryology for neurology and Neurosurgery residents

1. DEVELOPMENT OF BRAIN
AND SPINAL CORD
DR.SAMEEP KOSHTI

3. 7-12 days

4. BILAMINAR DISC = Epiblast (Near amniotic cavity) and Hypoblast(near yolk sac)

5. FROM HYPOBLAST  PRECHORDAL PLATE ROSTRALLY AND CLOACAL MEMBRANE CAUDALLY
13-15 days

6. GASTRULATION STARTS :
TRILAMINAR DISC FORMATION BY INTERPOSITION OF MESOBLASTIC CELL LAYER (15
days)

7. Primitive streak starts form cloacal membrane  primitive groove
Promitive node/hensen’s node  primitive pit

8. MESOBLAST :
Goes all the way rostrally to
the prechordal plate and
forms the SOLID ROD that is
Called NOTOCHORD
Also the Paraaxial mesoderm
Is formed

9. APPLIED:
related to occult spinal dysraphism
1.Neuroenteric cyst
2.split cord malformation
3.combined anterior and posterior
spina bifida

10. NEURULATION
 PRIMARY :
BRAIN AND SPINAL CORD TILL L1
APPLIED : OPEN DYSRAPHISM
 SECONDARY:
 DISTAL TO L1
 TWO STAGES:
 CANALIZATION OF CORD
 REGRESSION
 APPLIED : CLOSED SPINAL DYSRAPHISM

11. NEURAL TUBE
 LIES DORSAL TO NOTOCHORD
 TWO OPENINGS:
 ROSTRAL : ANTERIOR NEUROPORE AT LAMINA TERMINALIS
 CAUDAL : POSTERIOR NERUOPORE AT L1-2 cord level
 AMNIOTIC FLUID NOURISHES THE NEURAL TUBE THROUGH PORES
 CLSOES AT THE END OF 4 WEEKS
 ROSTRAL END OF NEURAL TUBE HAS THREE DILATATIONS
 Two constrictions
 4 cavities : TELE /DI /MESEN /HIND BRAIN
 Three flexures
 Early : Two at one month
 Cervical : b/w Rhomben and S.cord
 Cephalic(Midbrain) : b/e Midbrain and Rhomben
 Late: One at 6 weeks
 Pontine : b/w metencephalon and myelencephalon

16. DORSAL ALAR LAMINA
VENTRAL
BASAL LAMINA

17. Myelencephalon development

19. MESENCEPHALON DEVELOPMENT
• DIVIDED BY AQUEDUCT INTO
• DORSAL : TECTUM OF MIDBRAIN
• VENTRAL : AGAIN TWO subdivision
• Dorsal midbrain tegmentum
• Crus cerebri
• HAS TWO LAMINA
• ALAR LAMINA : 5th CN
• BASAL LAMINA : 3rd and 4th CN

20. DIENCEPHALON DEVELOPMENT
• IT IS A PART OF PROCECEPHALON CAUDAL TO THE INTERVENTRICULAR FORAMEN
• Has Only ALAR LAMINA
• TWO LATERAL WALL:
• Has hypothalamic sulcus :
• Ventral
• Hypothalamic nucleus
• Dorsal
• Anterior : Thalamus
• Posterior : Metathalamus (MGB AND LGB)
• THIN ROOF PLATE:
• Rostral:
• Form choroid plexus of third ventricle
• Caudal:
• Epithalamus : Pineal body + posterior commissure + habenular commissure and nuclei
• FLOOR PLATE:
• Anteriorly :
• Fuses with the Rathke’s pouch
• Forms the posterior lobe of the pituitary
• Posteriorly:
• Mamillary bodies

21. TELENCEPHALON DEVELOPMENT
• CEREBEAL VESICLES : forms hemispheres
• CAVITIES :
• Lateral ventricles
• Pallial tissue of the developing cerebral hemispheres
• Three zone layers: inside out
• Ependymal: Migrates outwards to form
neuronal and glial cells
• Mantle : forms the white matter
• Marginal : forms the cortical plate

22. NEURAL CREST DERIVATIVES

25. SECONDARY NEURULATION
• TWO STAGES:
• 1.Canalization of tail bud
• Day 28 to 48
• Caudal cell mass derived from the primitive streak forms vacuoles and forms caudal
neural tube
• Fuses with the proximal neural tube (formed by primary neurulation)
• APPLIED:
• Occult spinal dysraphism : L-S Lipoma and Lipomyelomeningocele
originate during these period
• 2.Regression of retrogressive differentiation :
• Filum terminale and cauda equina formed from caudal
neural tube and CONUS MEDDULARIS COMES TO LIE AT ITS ADULT LEVEL BY
REGRESSION
• Starts fro 43- 48 days and continue till early postnatal life

27. • VENTRICULUS TERMINALIS
• localized dilatation of central canal of Conus Medullaris
• IT ASCENDS by:
• Regrression of caudal neural tube
• Disproportionate growth of Vertebral column
• Resulting in Formation of the filum terminale
• Conus At birth :
• Conus lies opposite L3
• Conus at 3rd month of life :
• L1-2 interspace
• When conus is lower down :
• Lumbar and sacral nerve roots exit directly opposite
• When conus ascends:
• These nerve roots gets elongated and forms the cauda equina nerve
roots
• APPLIED:
• TIGHT FILUM TERMINALE resulting into TETHERED CORD
When conus is lower
down

30. MENINGES DEVELOPMENT
In the spine and in the cranium up to the midbrain:
 from the paraxial mesenchyme.
overlying the cerebral hemispheres
 from the neural crest.
The dura mater -- the pachymeninges, and the
pia and arachnoid, -- together, constitute the leptomeninges.
All the three meningeal layers :
 derived from a loose mesenchyme known as the meninx primitiva or primary meninx that
surrounds the primitive neural tube.
 Once the cerebrospinal fluid starts egressing from the ventricles it passes through the meninx
primitiva and separates the meninx primitiva into the pia mater and arachnoid.

31. THANK YOU