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Development of Nervous System (Special Embryology)
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- 2. NEURAL TUBE • Neuralplate: 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 • Itis 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 lowerend 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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- 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. Dr.Sherif Fahmy
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- 13. Development of Brain (Page175) Dr.Sherif Fahmy
- 14. Brain Vesicles andFlexures 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 Mesencephalicflexure Spinal cord Medulla Pons Midbrain telencephalon Dr.Sherif Fahmy
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- 20. Upper Part ofMedulla 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
- 21. Lower part ofMedulla 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
- 22. Fate of BasalLamina 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 Dr.Sherif Fahmy
- 23. Fate of AlarLamina - 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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- 28. Site: In thedorsal 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 caudalportion 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
- 30. Cervical flexure Pontine flexure Mesencephalicflexure Dr.Sherif Fahmy
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- 34. A- Development ofDiencephalon 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 ofCerebral 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 willexpands 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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- 40. Congenital anomalies ofbrain • 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
- 41. 7- Holoprosencephaly:Holoprosencephaly:Malformations ofmidline 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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