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DEVELOPMENT OF NERVOUS
SYSTEM
Dr.Sherif Fahmy
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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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Dr.Sherif Fahmy
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Dr.Sherif Fahmy
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Dr.Sherif Fahmy
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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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Dr.Sherif Fahmy
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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
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Dr.Sherif Fahmy
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Dr.Sherif Fahmy
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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
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Dr.Sherif Fahmy
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Development of Brain(Page 175)
Dr.Sherif Fahmy
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Brain Vesicles and FlexuresBrain Vesicles:1- Forebrain.2- Midbrain.3- Hindbrain.Flexures:1- Mesencephalic.2- Pontine.3- Cervical.
Dr.Sherif Fahmy
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Dr.Sherif Fahmy
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Cervical flexurePontine flexure
Mesencephalic flexure
Spinal cord
Medulla
Pons
Midbrain
telencephalon
Dr.Sherif Fahmy
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Development of Brain Stem
Dr.Sherif Fahmy
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Sagittal Section
Dr.Sherif Fahmy
Dr.Sherif Fahmy
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Dr.Sherif Fahmy
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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
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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
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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
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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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Dr.Sherif Fahmy
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Development of Cerebellum
Dr.Sherif Fahmy
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Shape
Dr.Sherif Fahmy
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Flocculus
NoduleLower SurfacePostero-lateral fissure
Dr.Sherif Fahmy
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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
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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
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Cervical flexurePontine flexure
Mesencephalic flexure
Dr.Sherif Fahmy
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Dr.Sherif Fahmy
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Dr.Sherif Fahmy
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Development of Forebrain
(Prosencephalon)(Page 181)
Dr.Sherif Fahmy
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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
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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
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-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
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Dr.Sherif Fahmy
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Dr.Sherif Fahmy
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Dr.Sherif Fahmy
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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
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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
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Hydrocephalus
Dr.Sherif Fahmy
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Microcephaly
Dr.Sherif Fahmy
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Exencephaly
Dr.Sherif Fahmy
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Arnold-Chiari Malformation
Dr.Sherif Fahmy
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Schizencephaly
Dr.Sherif Fahmy
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Holopros-encephaly
Dr.Sherif Fahmy
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Meningoencephalocele
Dr.Sherif Fahmy