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CNS DEVELOPMENT

CNS DEVELOPMENT. Stages in Neural Tube Development. Neural plate. Neural folds. Neural tube. Time-Line. Formation of nervous system occurs during the embryonic stage: End of second week to end of eighth week. Time-Line. Superior (anterior or cranial) neuropore closes by day 27.

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CNS DEVELOPMENT

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  1. CNS DEVELOPMENT

  2. Stages in Neural Tube Development • Neural plate. • Neural folds. • Neural tube.

  3. Time-Line • Formation of nervous system occurs during the embryonic stage: End of second week to end of eighth week.

  4. Time-Line • Superior (anterior or cranial) neuropore closes by day 27. • Inferior (posterior or caudal) neuropore closes by day 30.

  5. Subdivision of Cranial End of Neural Tube • Tripartite brain. • Pentapartite brain.

  6. Tripartite Brain • Prosencephalon. • Mesencephalon. • Rhombencephalon.

  7. Pentapartite Brain • Prosencephalon: Telencephalon (most anterior). Diencephalon. • Mesencephalon. • Rhombencephalon: Metencephalon. Myelencephalon.

  8. Telencephalon Primordia • Lumina: Lateral ventricles (I, II). • Floor: Basal ganglia (nuclei). Olfactory lobes and nerves. • Roof: Cerebral hemispheres.

  9. Diencephalon Primordia • Lumen: Third ventricle. • Roof: Epithalamus. • Walls: Thalamus. • Floor: Hypothalamus and infundibulum.

  10. Mesencephalon Primordia • Lumen: Cerebral aqueduct (of Sylvius). • Roof =Tectum: Superior and inferior colliculi. • Floor: Tegmentum.

  11. Metencephalon Primordia • Lumen: Part of fourth ventricle. • Roof: Cerebellum. • Floor: Pons.

  12. Myelencephalon Primordia • Lumen: Rest of fourth ventricle. • Main part: Medulla oblongata. • Roof: Posterior choroid plexus.

  13. Histogenesis of Neural Tube • Initial tube wall = Pseudostratified epithelium: Single layer of cells, but cells are of different heights. All cells are in contact with a basement membrane. • Outermost membrane = External limiting membrane.

  14. Histogenesis of Neural Tube • Some neuroepithelial cells remain attached to the basement membrane and will form a single layer of ependymal cells that will line the entire ventricular system and the neural canal.

  15. Histogenesis of Neural Tube • Tube differentiates into two concentric rings by day 26: Mantle layer and marginal layer.

  16. Histogenesis of Neural Tube • Other cells lose contact with the basement membrane and will migrate past the ependymal cells to form a new outer layer of densely packed cells collectively called the: Mantle layer: • Cells that make up the mantle layer are: NEUROBLASTS. • Note that mantle layer is still covered by the external limiting membrane.

  17. Histogenesis of Neural Tube • Neuroblasts in the mantle layer will begin to grow processes (axons) that will form a new outer layer: Marginal layer. The marginal layer is also located beneath the external limiting membrane. • The marginal layer will form the white matter of the spinal cord and the brain. • The mantle layer forms the gray matter of the brain and spinal cord (except for the cortices).

  18. DEVELOPMENTAL ANOMALIES

  19. Anencephaly • Failure of cranial end of neural tube to close.

  20. Arnold-Chiari deformity • Inferior cerebellum and medulla are elongated and protrude into vertebral canal. • Medulla and pons are small and deformed. • Hydrocephalus. • Malformation of lower cranial nerves: Deafness. Tongue, facial muscle, lateral eye movement weakness.

  21. Spina Bifida Occulta • Results from a failure of the inferior neuropore to close. • Vertebral arch(-es) fails to develop in caudal area. • Spinal cord function is usually normal.

  22. Spina Bifida Cystica • Characterized by a sac-like cyst at the caudal end of spine. • Spinal cord and/or meninges may be found in the cyst. • Spinal cord function may be impaired. • May be lower extremity dysfunction. • Bladder and bowel function may be impaired.

  23. Meningocele • Form of spina bifida cystica. • Only meninges found in sac. • Spinal cord function may be impaired. • Signs and symptoms vary depending on location and severity of malformation.

  24. Meningomyelocele • Form of spina bifida cystica. • Both meninges and spinal cord are found in sac. • Always results in abnormal growth of spinal cord. • Lower extremity paralysis. • Bowel and bladder dysfunction. • Loss of sensation to lower limbs.

  25. Myeloschisis • Failure of caudal neural folds to close. • Most severe of the defects.

  26. Holoprosencephaly • Failure of prosencephalon to divide into two cerebral hemispheres. • Often associated with facial deformities: Single orbit with two eyes or one eye or no eye. Proboscis-type nose located above eye. Cleft lip and palate.

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