1 / 31

SECOND WEEK

SECOND WEEK. Differentiation of the embryo into three germ layers : Ectoderm . Mesoderm . Endoderm . The Ectoderm will form (1) Central nervous system. (2) Epidermis of Skin. THIRD WEEK. Neural Plate :

joella
Download Presentation

SECOND WEEK

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. SECOND WEEK Differentiation of the embryo into three germ layers : • Ectoderm. • Mesoderm. • Endoderm. • The Ectodermwill form • (1) Central nervous system. • (2) Epidermis of Skin.

  2. THIRD WEEK • Neural Plate : • It is a dorsal midline thickening of the ectoderm overlying the notochord (Neuroectoderm) .

  3. THIRD WEEK • Neural Folds : • They are the elevated lateral margins of the neural plate. • They are on each side of the longtudinal midline (Neural Groove).

  4. NEURAL TUBE • It is formed from the apposition and fusion of the neural folds which seal the neural groove and create the tube.

  5. FOURTH WEEK • The neural tube is completed and transformed into the adult CNS. • This growth is maximal at the rostral part which becomes the brain. • The caudal portion becomes the spinal cord. • The axis of the neural tube (neuroaxis) is straight.

  6. NEURAL GROOVE • The central cavity within the neural tube becomes : • Ventricles of the brain and • Central canalof the spinal cord.

  7. NEURAL CREST • They are separated cells from the apices of the neural folds. • They are dorsolateral to the neural tube. • They give rise to : • Autonomic ganglia. • Sensory ganglia of spinal and cranial nerves. • Melanocytes. • Cells of supra renalmedulla.

  8. DIFFERENTIATION OF SPINAL CORD • The Grey matter is located centrally around the central canal. • The White matter forms the outer coat.

  9. DIFFERENTIATION OF SPINAL CORD • SulcusLimitans : • It is a longtudinal groove along the inner surface of the lateral walls of the developing spinal cord. • It differentiates the grouping of cells (gray matter) into dorsal (Alar) plate and a ventral (Basal) plate.

  10. DIFFERENTIATION OF SPINAL CORD • The Alar plate is predominantly sensory in function. • The Basal plate is predominantly motor in function.

  11. DIFFERENTIATION OF BRAIN • 5th week: • Three primary brain vesicles appear : • Fore brain (Prosencephalon). • Mid brain (Mesencephalon). • Hind brain (Rombencephalon).

  12. FLEXURES • The neuraxis is bent by two flexures : • Cephalic( Midbrain)flexure at the junction of the fore and mid brains. • Cervical flexure : • Between the brain and spinal cord.

  13. SEVENTH WEEK • Fivesecondary brain vesicles appear.

  14. PROSENCEPHALON • Is divided into : • Telencephalon. • Diencephalon.

  15. TELENCEPHALON • It is the largest brain vesicle. • It has the greatest degree of development. • It forms the two Cerebral Hemispheres.

  16. DIENCEPHALON • It is formed mainly of the Thalamus. • The Thalamus contains numerous groups of neurons and is connected with the cerebral cortex.

  17. ROMBENCEPHALON • Is divided into : • Metencephalon. • Mylencephalon.

  18. PONTINE FLEXURE • It is the third flexure that appears between the metencephalonand the myelencephalon.

  19. METENCEPHALON • It is differentiated into: • Pons . • Cerebellum.

  20. MYELENCEPHALON • It will form : • The Medulla Oblongata.

  21. MESENCEPHALON • It remains undifferentiated. • It is in the form of its embryonic picture : • Central canal surrounded by grey matter.

  22. BRAIN CENTERS • They consist of : • Bilateral paired centers for the senses of : • Smell, Vision,Hearing and • A symmetricalmidlineVestibular center for the maintenance of equilibrium.

  23. BRAIN CENTERS • They start to appear as expansions from the dorsal aspect of the simple tubular brain. • They are composed of an outer cortex of nerve cells with underlying core of nerve fibers.

  24. BRAIN CENTERS • The centers for vision and hearing will form largely automatic, reflex functions. • They are represented by the four colliculi(superior & inferior). • The motor center near the caudal end of the brain will be in the cerebellum.

  25. PROSENCEPHALISATION • The massive cerebral hemispheres which are developed from the rostral (olfactory) part of the brain take an executive role in many functions of the brain.

  26. PROSENCEPHALISATION • They become the highest levels for perception and correlation ofall sensory modalities • They are the highest level for motor control. • The other centers become progressively subservient to the cerebral hemispheres.

  27. CONGENITAL ANOMALIES • (1) Anencephaly • The brain and skull are minute. • It is incompatible for life.

  28. (2) SPINA BIFIDA • It is underdevelopment of the lower part of the spinal cord and the nerve roots. • It may be associated with underdevelopment of the bone and skin.

  29. SPINA BIFIDA • The infants with Spina Bifida complain from : • Paralysed, anesthetic lower limbs. • Incontinence of urine and stool.

  30. (3) MENINGIOMYELOCELE • It is Spina Bifida with • The appearance of the meninges of the spinal cord on the back of the body.

More Related