Development of Nervous System

1. DEVELOPMENT
OF NERVOUS
SYSTEM
Dr.Sherif Fahmy

2. NEURAL TUBE
• Neural plate: is formed from thickened
ectoderm between primitive node and bucco-
pharyngeal membrane.
• Neural tube: fusion of neural folds at the
middle of the plate then extends cranio-
caudaly till the closure of anterior neuropore
(at 23th day) and posterior neuropore (at 25th
day).
Dr.Sherif Fahmy

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6. SPINAL CORD
• It is developed from caudal part of neural tube.
Firstly the neural tube is formed of a single layer
which proliferates to form middle mantle layer with
lining ependymal layer. Marginal layer is nerve
axons that lie outside the mantle.
• Mantle layer will be differentiated into ventral basal
lamina a dorsal alar lamina. This demarcation
appears on the inner surface of neural as sulcus
limitans.
• Basal lamina forms anterior horn cells and alar
lamina forms posterior horn cells.
Dr.Sherif Fahmy

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8. Level of lower end of spinal cord
• Firstly, spinal cord occupies the
whole length of vertebral canal.
• At birth: It lies at level of L3 vertebra.
• In adults: It terminates at disc
between L1/L2 verterbra.
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11. Congenital Anomalies
• 1- Spina bifida oculta: defective formation of
lamina of vertebra.
• 2- Spina bifida with meningeocele:
protrusion of meninges through the laminar
defect.
• 3- Spina bifida with meningeomyelocele:
with protrusion of spinal cord and meninges.
• 4- Rachischisis: defective closure of neural
tube and lamina of vertebrae.
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13. Development of Brain
(Page 175)
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14. Brain Vesicles and Flexures
Brain Vesicles:
1- Forebrain.
2- Midbrain.
3- Hindbrain.
Flexures:
1- Mesencephalic.
2- Pontine.
3- Cervical. Dr.Sherif Fahmy

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16. Cervical flexure
Pontine flexure
Mesencephalic flexure
Spinal
cord
Medulla
Pons
Midbrain
telencephalon
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17. Development of Brain
Stem
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18. Sagittal Section
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20. Upper Part of Medulla and Pons
-Cavity is widened to form 4th
ventricle.
-Roof plate will form roof of 4th
ventricle.
-Alar lamina becomes lateral to basal
lamina.
-Dorsal edge of alar lamina of pons will
form superior rhombic lip.
-Dorsal edge of alar lamina of medulla
will form inferior rhombic lip.
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21. Lower part of Medulla and Midbrain
-The cavity remains as central canal.
-Alar lamina is lateral to basal lamina.
Then the alar and basal laminae will
give rise to the following nuclei.
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22. Fate of Basal Lamina
General somatic efferent (GSE): Form motor nuclei of
3rd
, 4th
, 6th
and 12th
cranial nerves.
Special visceral efferent (SVE): Forms motor nuclei of
trigeminal, facial, 9th
, 10th
and 11th
.
General Visceral efferent: Edinger-westphal n. of
oculomotor, superior salivary of facial n., inferior
salivary nuscleus of glossopharyngeal n and dorsal
nucleus of vagus
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23. Fate of Alar Lamina
- General visceral and special visceral
afferent: which form nucleus solitarius
(Taste) in medulla.
- General somatic afferent: will form
mesencephalic, main sensory nucleus
and spinal neuclus of trigeminal nerve.
- Special somatic afferent: vestibular
and cochlear nuclie Dr.Sherif Fahmy

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25. Development of
Cerebellum
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26. Shape
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27. Flocculus
Nodule
Lower Surface
Postero-
lateral
fissure
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28. Site: In the dorsal wall of hindbrain.
Cells: Ectodermal cells of neural tube.
Steps:
1- Formation of 2 cerebellar swellings from
superior rhombic lip.
2- Fusion between the cerebellar swellings that
covers the roof of 4th
ventricle.
3- The developing cerebellum is divided into
cranial & caudal portions by posterolateral
fissure.
Dr.Sherif Fahmy

29. 4- The caudal portion will form
flocculonodular lobe.
5- The cranial portion will grows faster to
form rest of cerebellum (2 cerebellar
hemisphers and vermis).
6- Development of primary fissure between
anterior & posterior lobes, Development of
transverse fissures and folia to increase the
surface area.
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30. Cervical flexure
Pontine flexure
Mesencephalic flexure
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33. Development of
Forebrain
(Prosencephalon)
(Page 181)
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34. A- Development of Diencephalon
Site: In the cranial portion of neural tube.
Cells: Ectodermal cells.
Steps:
1- The roof plate is thin and invaded by choroid plexus.
2- The floor plate is thickened and divided into posterior
larger part which forms hypothalamus and anterior smaller
part which gives rise to posterior lobe of pituitary gland.
3- Basal plate is lacking.
4- Alar plate will form thalamus, rest of hypothalamus and
epithalamus.
5- Cavity will be the 3rd
ventricle.
Dr.Sherif Fahmy

35. B- Development of Cerebral
Hemisphere
-Cerebral hemispheres are developed from
telencephalon of the forebrain.
-The cavity will be lateral ventricles.
-Neuroblasts migrate externally to form
cerebral cortex while some cells remain near
the base to form basal ganglia.
-Axons from neuroblasts in cortex will form
internal capsule that split corpus striatum into
caudate and lentiform nuclei.Dr.Sherif Fahmy

36. -Cerebral cortex will expands forewards,
backwards, laterally and downwards to
form cerebral lobes.
-Insula is formed as this part of cortex will
grow slowly whereas the surroundings
grow faster and cover it, forming
opercula.
-At first the cerebral cortex is smooth but
later in fetal life it grows and expands to
form sulci and gyri.
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40. Congenital anomalies of brain
• 1- Anencephaly:Anencephaly: defective formation of skull cap
with exposed malformed brain.
• 2- Hydrocephalus:Hydrocephalus: distension of ventricles due to
accumulation of CSF.
• 3- Microcephaly:Microcephaly: Small sized brain and skull.
• 4- MeningoceleMeningocele: protrusion of meninges through
skull defect.
• 5- Meningo-encephalocele:Meningo-encephalocele: protrusion of meninges
and brain tissue.
• 6- Meningo-hydro-encephalocele:Meningo-hydro-encephalocele: protrusion of
meninges, brain tissue and dilated ventricles.
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41. 7- Holoprosencephaly:Holoprosencephaly:Malformations of midline
structures of head in brain and face.
8- Schizencephaly:Schizencephaly: Large cleft in cerebral
hemisphere.
9- Arnold-Chiari malformation:Arnold-Chiari malformation: caudal herniation
of cerebrum through foramen magnum.
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42. Hydrocephalus
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43. Microcephaly
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44. Exencephaly
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45. Arnold-Chiari Malformation
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46. Schizencephaly
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47. Holopros-
encephaly
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48. Meningoencephalocele
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