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DEVELOPMENT OF THE CNS

DEVELOPMENT OF THE CNS. DR JAMILA ELMEDANY. NEURO ECTODERM. It is the source of the Central nervous system. It is derived from: Ectoderm which is Differentiated in the 2 nd Week. NEUROECTODERM (THIRD WEEK) . Neural Plate :

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DEVELOPMENT OF THE CNS

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  1. DEVELOPMENT OF THE CNS DR JAMILA ELMEDANY

  2. NEURO ECTODERM It is the source of the Central nervous system. It is derived from: Ectodermwhich is Differentiated in the2ndWeek.

  3. NEUROECTODERM (THIRD WEEK) • Neural Plate : • A Dorsal Midline Thickening of the Ectoderm overlying the Notochord. • Neural Folds : • Elevated Lateral Margins of the Neural Plate. • They are on each side ofNeural Groove(Longitudinal Midline Groove).

  4. NEUROECTODERM (THIRD WEEK) • Neural Tube: • Apposition and Fusion of the Neural Folds. • They seal the Neural Groove and Create the Tube.

  5. CNS (FOURTH WEEK) • Growth of the Neural tube is Maximal at the Cranial Part. • It becomes the Brain. • The Caudal Part becomes: • Spinal Cord. • Neuroaxis : • Axis of the tube is Straight.

  6. NEURAL GROOVE • Central Cavity within the Neural Tube. • Differentiates into: • Ventricles of the Brain. • Central Canalof the Spinal Cord.

  7. NEURAL CREST CELLS • Separated Cells from the Apices of the Neural Folds. • Position: • Dorsolateral to the Neural Tube. • Give rise to : • 1. Autonomic Ganglia. • 2. Sensory Ganglia of Spinal and Cranial nerves. • 3. Melanocytes. • 4. Cells of Suprarenal Medulla.

  8. INTERNAL STRUCTURE OF SC • Grey matter:Located Centrally around the Central Canal. • White matter: • Forms the Outer Coat.

  9. SULCUS LIMITANS • A longitudinal Groove along the Inner surface of the Lateral Walls of thedeveloping Spinal Cord. • It differentiates the Gray Matter into: • Dorsal (Alar) plate. • It is predominantly Sensory. • Ventral (Basal) plate. • It is predominantly Motor.

  10. FIFTH WEEK • Three Primary Brain Vesicles appear. • Fore Brain (Prosencephalon). • Mid Brain (Mesencephalon). • Hind Brain (Rombencephalon).

  11. FLEXURES • Bending of the Neuraxis is by Two FLexures : • Cephalic( Midbrain)Flexure: • At the junction of the Fore and Mid Brains. • Cervical Flexure : • Between the Brain and Spinal Cord.

  12. SEVENTH WEEK • Five Secondary Brain Vesicles appear. • Formed by Division of • Prosencephalon into: • Telencephalon. • Diencephalon.

  13. TELENCEPHALON • Largest Brain Vesicle. • Has the Greatest Degree of Development. • Forms: • The Cerebral Hemispheres.

  14. DIENCEPHALON • Thalamusis its Main Part. • It is connected to the Cerebral Cortex.

  15. ROMBENCEPHALON • Differntiated into : • Metencephalon. • Mylencephalon.

  16. PONTINE FLEXURE • The Third Flexure. • Appears between:Metencephalonand Myelencephalon.

  17. DIFFERENTIATION • Metencephalon: • Pons . • Cerebellum. • Myelencephalon: • Medulla Oblongata.

  18. MESENCEPHALON • Remains Undifferentiated. • It keeps the Embryonic Picture : • Grey Matter surrounds the Central canal.

  19. BRAIN CENTERS • (1) Bilateral pairedFor the senses of : • Smell. • Vision. • Hearing. • (2) A symmetrical midline: • VestibularcenterFor the maintenance of Equilibrium.

  20. DEVELOPMENT OF THE CENTERS • They are Expansions from: • Dorsal Aspectof the simple Tubular Brain. • Composed of : • Outer Cortex of NerveCells. • Underlying Core of Nerve Fibers.

  21. REFLEX CENTERS • Centers for Vision and Hearing will have Automatic Reflex Functions. • These are represented by: Superior & Inferior Colliculi.

  22. PROSENCEPHALISATION • The massive cerebral hemispheres will take an Exclusive Role in many functions of the brain. • They become: • The Highest Levels for: Perception and Correlation ofall Sensory Modalities. • The Highest Level for Motor Control. • Other Centers: • Become progressively Subservient to the Cerebral Centers.

  23. CONGENITAL ANOMALIES • (1) Anencephaly • The Brain and Skull are minute. • Incompatible for living.

  24. (2) SPINA BIFIDA • Underdeveloped Lower part of the Spinal Cord and the Associated Nerve Roots. • It may be associated with underdevelopment of the Bone and Skin.

  25. MANIFESTATIONS • Anesthetic Lower Limbs. • Paralysis. • Incontinence of urine and stool.

  26. CONGENITAL ANOMALIES • (3) Meningomyelocele: • It is Spina Bifida with • The appearance of the Meninges of the Spinal Cord on the Back of the Body.

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