DEVELOPMENT OF NERVOUS

SYSTEM

Dr.Sherif Fahmy

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

Dr.Sherif Fahmy

Dr.Sherif Fahmy

Dr.Sherif Fahmy

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

Dr.Sherif Fahmy

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.

Dr.Sherif Fahmy

Dr.Sherif Fahmy

Dr.Sherif Fahmy

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.

Dr.Sherif Fahmy

Dr.Sherif Fahmy

Development of Brain(Page 175)

Dr.Sherif Fahmy

Brain Vesicles and FlexuresBrain Vesicles:1- Forebrain.2- Midbrain.3- Hindbrain.Flexures:1- Mesencephalic.2- Pontine.3- Cervical.

Dr.Sherif Fahmy

Dr.Sherif Fahmy

Cervical flexurePontine flexure

Mesencephalic flexure

Spinal cord

Medulla

Pons

Midbrain

telencephalon

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Development of Brain Stem

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Sagittal Section

Dr.Sherif Fahmy

Dr.Sherif Fahmy

Dr.Sherif Fahmy

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.

Dr.Sherif Fahmy

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.

Dr.Sherif Fahmy

Fate of Basal LaminaGeneral 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

Dr.Sherif Fahmy

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

Dr.Sherif Fahmy

Development of Cerebellum

Dr.Sherif Fahmy

Shape

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Flocculus

NoduleLower SurfacePostero-lateral fissure

Dr.Sherif Fahmy

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

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.

Dr.Sherif Fahmy

Cervical flexurePontine flexure

Mesencephalic flexure

Dr.Sherif Fahmy

Dr.Sherif Fahmy

Dr.Sherif Fahmy

Development of Forebrain

(Prosencephalon)(Page 181)

Dr.Sherif Fahmy

A- Development of DiencephalonSite: 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

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

-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. Dr.Sherif Fahmy

Dr.Sherif Fahmy

Dr.Sherif Fahmy

Dr.Sherif Fahmy

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.

Dr.Sherif Fahmy

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.

Dr.Sherif Fahmy

Hydrocephalus

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Microcephaly

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Exencephaly

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Arnold-Chiari Malformation

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Schizencephaly

Dr.Sherif Fahmy

Holopros-encephaly

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Meningoencephalocele

Dr.Sherif Fahmy