1. 1Prof. Saeed makarem

2. Prof. Saeed Makarem 2 secondthree By the beginning of the second week, three germ cell layers become established: Ectoderm, Mesoderm and Endoderm. EARLY DEVELOPMENT

3. Prof. Saeed makarem 3 Each germ layer gives rise to particular tissues and organs in the adult.

4. 4 The Ectoderm gives rise to: 1- Epidermis of the Skin 2- Nervous system. Prof. Saeed makarem

5. 5 Mesoderm The Mesoderm forms: 1-Skeleton, 2-Muscular tissues 3-Connective tissues.

6. Prof. Saeed makarem 6 Endoderm The Endoderm gives rise: to the: 1-Alimentary, 2- Respiratory 3-Genitourinary tracts.

7. 7 During the 3 rd week ectodermDuring the 3 rd week, the dorsal midline ectoderm undergoes thickening to form the neural plate. The lateral margins of the neural plate become elevated, forming neural folds. In between the two neural folds a longitudinal, midline depression, will form the neural groove. The neural folds then become apposed and fuse together. Now the neural groove is transformed into the neural tube. Prof. Saeed makarem

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9. 9 Some cells from the apices of the neural folds become detached to form groups of cells lying dorsolateral to the neural tube. These are known as the neural crests. By the middle of the fourth week the formation of the neural tube is completed.

10. Prof. Saeed makarem 10 Enormous growth, distortion & cellular differentiation occur in the neural tube. This is maximal in the rostral part, which develops into the brain, while the caudal part will forms the spinal cord. DEVELOPMENT OF THE BRAIN & SPINAL CORD

11. Prof. Saeed makarem 11 The central cavity within the neural tube becomes: The ventricles of the brain & The central canal of the spinal cord.

12. Prof. Saeed makarem 12 The neural crests cells form the sensory ganglia of the spinal & cranial nerves, and also the autonomic ganglia.

13. Prof. Saeed makarem 13 As development continues, a longitudinal groove, called the sulcus limitans, appears on the inner surface of the lateral walls of the embryonic spinal cord and caudal part of the brain. The dorsal and ventral cell groupings thus forming the alar plate and the basal plate, respectively.

14. Prof. Saeed makarem 14 sensory functions, motor. Nerve cells that develop within the Alar plate have predominantly sensory functions, while those in the basal plate are predominantly motor.

15. Prof. Saeed makarem 15 Further development also brings about the differentiation of grey and white matter. The grey matter is located centrally around the central canal, While the white matter forming an outer coat.

16. Prof. Saeed makarem 16 This basic developmental pattern can still easily be recognized in the adult spinal cord.

17. Prof. Saeed makarem 17 DEVELOPMENT OF THE BRAIN During development, the rostral portion of the neural tube undergoes massive differentiation and growth to form the brain. By the 5 th week three primary brain vesicles By the 5 th week, three primary brain vesicles can be identified: 1. Prosencephalon or (forebrain), 2. Mesencephalon or (midbrain), 3. Rhombencephalon or (hindbrain).

18. Prof. Saeed Makarem 18 The longitudinal axis of the developing CNS does not remain straight but is bent by : 1- Cephalic, or Midbrain flexure occurring at the junction of the forebrain and midbrain 2-Cervical flexure between the brain and the spinal cord.

19. 19 five By the 7 th week further differentiation distinguishes five secondary brain vesicles produced by: Division of the prosencephalon into 2 lateral vescicle the telencephalon and a median part the diencephalon. Also, division of the rhombencephalon into the metencephalon and myelencephalon. Prof. Saeed makarem

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21. 21 The junction between the metencephalon and the myelencephalon is marked by an additional bend in the neuraxis, called the The junction between the metencephalon and the myelencephalon is marked by an additional bend in the neuraxis, called the pontine flexure. Prof. Saeed makarem

22. 22 Lateral V Aqueduct of Midbrain 4 th Vent. 3 rd.V cavity

23. 23 FURTHER DEVELOPMENT OF THE BRAIN ProsencephalonOf the three basic divisions of the brain, the Prosencephalon or forebrain is by far the largest. cerebrum.It is also referred to as the cerebrum. ProsencephalonOf the three basic divisions of the brain, the Prosencephalon or forebrain is by far the largest. cerebrum.It is also referred to as the cerebrum. Prof. Saeed makarem

24. 24 The telencephalon undergoes the greatest further development and gives rise to the two cerebral hemispheres. Prof. Saeed makarem

25. 25 The cerebral hemispheres consist of: Outer layer of grey matter (the cerebral cortex) Inner mass of white matter, within which various groups of grey matter nuclei are buried Prof. Saeed makarem

26. 26 The Mesencephalon, or midbrain, is relatively undifferentiated, (it still retains a central tube-like cavity surrounded by grey matter).

27. Prof. Saeed makarem 27 The metencephalon develops into the Pons anteriorly & cerebellum posteriorly.

28. Prof. Saeed makarem 28 The myelencephalon forms the medulla oblongata.

29. Prof. Saeed makarem 29 As the brain develops, its central cavity also undergoes considerable changes in size and shape forming a system of ventricles, which contain cerebrospinal fluid (CSF).

30. Prof. Saeed makarem 30 Disorders of development disrupt the normal growth and structural organization of the spinal cord and brain. ectoderm, Because the nervous system is derived from embryonic ectoderm, these developmental anomalies also involve the coverings of the nervous system (skin and bone). DEVELOPMENTAL ANOMALIES

31. Prof. Saeed makarem 31 ANENCEPHALY In anencephaly, the brain and skull are minute and the infant does not usually survive.

32. SPINA BIFIDA In spina bifida, the lower part of the spinal cord and nerve roots are underdeveloped and may lie uncovered by skin or the bony spine on the infant's back. Prof. Saeed Makarem 32

33. MENINGIOMYELOCELE It is Spina Bifida withIt is Spina Bifida with the meninges of the spinal cord appear on the back of the infant.the meninges of the spinal cord appear on the back of the infant. Such infants are left with flail, paralyzed and anaesthetic lower limbs together with incontinence of the bowel and bladder.Such infants are left with flail, paralyzed and anaesthetic lower limbs together with incontinence of the bowel and bladder.