1. EMBRYOLOGY OF CEREBRAL HEMISPHERE & CEREBELLUM
Prof. Mujahid Khan
اسم ورقم المقرر – Course Name and No.
7/13/2019

2. Neurulation
The process of formation of neural plate and neural folds and closure of the folds to form the neural tube is called neurulation
This process is completed by the end of the fourth week
When closure of the caudal (lower) neuropore occurs during neurulation, the embryo may be called as a neurula
اسم ورقم المقرر – Course Name and No.
7/13/2019

3. اسم ورقم المقرر – Course Name and No.
7/13/2019

4. Neural Plate and Neural Tube
The embryonic ectoderm over the notochord thickens to form an elongated, slipperlike plate of thickened epithelial cells called neural plate
The ectoderm of the neural plate (neuroectoderm) gives rise to the brain and spinal cord
On about 18th day, the neural plate invaginates along its central axis to form a longitudinal median neural groove
اسم ورقم المقرر – Course Name and No.
7/13/2019

5. اسم ورقم المقرر – Course Name and No.
7/13/2019

6. Neural Plate and Neural Tube
Neural groove has neural folds on each side
Neural folds become prominent at the cranial end of the embryo and are the first sign of brain development
By the end of the third week, the neural folds move together and fuse, converting the neural plate into a neural tube
Neural tube is a primordium of the CNS
اسم ورقم المقرر – Course Name and No.
7/13/2019

7. Development of Brain
Neural tube cranial (superior) to the fourth pair of somites develops into the brain
Fusion of the neural folds in the cranial region and closure of the rostral (upper) neuropore form three primary brain vesicles
Forebrain (prosencephalon)
Midbrain (mesencephalon)
Hindbrain (rhombencephalon)
اسم ورقم المقرر – Course Name and No.
7/13/2019

8. اسم ورقم المقرر – Course Name and No.
7/13/2019

9. Development of Brain
During fifth week, the forebrain partly divides into two secondary brain vesicles, telencephalon and diencephalon
Midbrain does not divide
Hindbrain partly divides into the metencephalon and myelencephalon
In total there are five secondary brain vesicles
اسم ورقم المقرر – Course Name and No.
7/13/2019

10. اسم ورقم المقرر – Course Name and No.
7/13/2019

11. Brain Flexures
During the fourth week, the embryonic brain grows rapidly and bends ventrally with the head fold
This produces a midbrain flexure in the midbrain region and cervical flexure at the junction of hindbrain and spinal cord
Later unequal growth of brain between these flexures produces the pontine flexure in the opposite direction
اسم ورقم المقرر – Course Name and No.
7/13/2019

12. اسم ورقم المقرر – Course Name and No.
7/13/2019

13. Hindbrain
Cervical flexure demarcates the hindbrain from the spinal cord
Pontine flexure located in the future pontine region, divides the hindbrain into caudal myelencephalon and rostral metencephalon parts
The myelencephalon becomes medulla oblongata
The metencephalon becomes the pons and cerebellum
The cavity of the hindbrain becomes the fourth ventricle and the central canal in the medulla
اسم ورقم المقرر – Course Name and No.
7/13/2019

14. اسم ورقم المقرر – Course Name and No.
7/13/2019

15. Myelencephalon
Caudal part of myelencephalon (closed part of medulla oblongata) resembles the spinal cord both developmentally and structurally
The neural canal of neural tube forms a central canal
Ventral area of the medulla contains a pair of fiber bundles called pyramids which consists of corticospinal fibers descending from the developing cerebral cortex
اسم ورقم المقرر – Course Name and No.
7/13/2019

16. Metencephalon The walls of metencephalon form the pons and cerebellum
Cavity of the metencephalon forms the superior part of the fourth ventricle
Pontine flexure causes divergence of the lateral walls of the pons which spreads the gray substance in the floor of the fourth ventricle
اسم ورقم المقرر – Course Name and No.
7/13/2019

17. اسم ورقم المقرر – Course Name and No.
7/13/2019

18. Metencephalon
Cerebellum develops from thickenings of dorsal parts of alar plates
Initially the cerebellar swellings project into the fourth ventricle
As the swellings enlarge and fuse in the median plane , they overgrow the rostral half of the fourth ventricle and overlap the pons and medulla
Some neuroblasts differentiate into the neurons of the cerebellar cortex
اسم ورقم المقرر – Course Name and No.
7/13/2019

19. اسم ورقم المقرر – Course Name and No.
7/13/2019

20. Choroid Plexus and CSF
The ependymal roof of the fourth ventricle is covered externally by pia mater derived from mesenchyme of the hindbrain
This vascular pia mater together with ependymal roof forms the tela choroidea
Due to active proliferation of pia mater the tela choroidea invaginates the fourth ventricle where it differentiates into choroid plexus
اسم ورقم المقرر – Course Name and No.
7/13/2019

21. اسم ورقم المقرر – Course Name and No.
7/13/2019

22. Choroid Plexus and CSF
Similar choroid plexuses develop in the roof of the third ventricle and medial walls of the lateral ventricles
Choroid plexus secrete cerebrospinal fluid
The thin roof of fourth ventricle evaginates in three locations
These outpouchings rupture to form openings, median foramen magendie and lateral foramina of Luschka
These foramina permit the CSF to enter the subarachnoid space from the fourth ventricle
اسم ورقم المقرر – Course Name and No.
7/13/2019

23. اسم ورقم المقرر – Course Name and No.
7/13/2019

24. اسم ورقم المقرر – Course Name and No.
7/13/2019

25. Midbrain
The midbrain (mesencephalon) undergoes less change except the caudal (lower) part
The neural canal narrows and becomes cerebral aqueduct
The canal connects the third and fourth ventricles
اسم ورقم المقرر – Course Name and No.
7/13/2019

26. Forebrain
As the rostral neuropore closes, two lateral outgrowths, optic vesicles appear on each side of the forebrain
Optic vesicles are primordia of the retinae and optic nerves
A second pair of diverticula arise dorsally and rostrally, are the telencephalic vesicles
These are primordia of cerebral hemispheres and their cavities become the lateral ventricles
اسم ورقم المقرر – Course Name and No.
7/13/2019

27. Forebrain
The rostral or anterior part of the forebrain, including primordia of cerebral hemispheres is telencephalon
The caudal or posterior part of the forebrain is the diencephalon
The cavities of the telencephalon and diencephalon contribute to the formation of the third ventricle
اسم ورقم المقرر – Course Name and No.
7/13/2019

28. Diencephalon
Three swellings develop in the lateral walls of the third ventricle, which later become the epithalamus, thalamus and hypothalamus
Thalamus is separated from the epithalamus by the epithalamic sulcus and from the hypothalamus by the hypothalamic sulcus
Thalamus develops rapidly on each side and bulges into the cavity of the third ventricle
اسم ورقم المقرر – Course Name and No.
7/13/2019

29. اسم ورقم المقرر – Course Name and No.
7/13/2019

30. اسم ورقم المقرر – Course Name and No.
7/13/2019

31. Telencephalon
Telencephalon consists of a median part and two lateral diverticula called cerebral vesicles
These diverticula are primordia of cerebral hemispheres
The cavity of the median portion of the telencephalon forms the anterior part of third ventricle
As cerebral hemispheres expand, they cover successively the diencephalon, midbrain and hind brain
اسم ورقم المقرر – Course Name and No.
7/13/2019

32. Telencephalon
The hemispheres eventually meet each other in the midline, flattening their medial surfaces
The mesenchyme trapped in the longitudinal fissure between them, a median fold of dura mater gives rise to falx cerebri
The growth and curvature of the hemispheres also affect the shape of the lateral ventricles
They become roughly C-shaped cavities filled with CSF
اسم ورقم المقرر – Course Name and No.
7/13/2019

33. اسم ورقم المقرر – Course Name and No.
7/13/2019

34. Telencephalon Initially the surface of the hemispheres is smooth
As growth proceeds, sulci and gyri develop
Sulci and gyri permit a considerable increase in the surface area of the cerebral cortex without requiring an extensive increase in cranial size
اسم ورقم المقرر – Course Name and No.
7/13/2019

35. Congenital Anomalies of Brain
Due to the complexity of its embryological history, abnormal developments of brain is common, about 3 per 1000 births
Major congenital anomalies of the brain are meroanencephaly and meningoencephalocele result from defective closure of rostral neuropore
Congenital anomalies of the brain may be caused by alterations in morphogenesis or histogenesis of nervous tissue
اسم ورقم المقرر – Course Name and No.
7/13/2019

36. اسم ورقم المقرر – Course Name and No.
7/13/2019

37. Congenital Anomalies of Brain
Congenital anomalies may result from developmental failures in associated structures like notochord, somites, mesenchyme and skull
Abnormal histogenesis of the cerebral cortex may result in seizures and various types of mental retardation
Anomalies occur due to the exposure of the fetus or embryo to certain viruses and high levels of radiation
اسم ورقم المقرر – Course Name and No.
7/13/2019

38. Common Anomalies of Brain
Cranium bifidum
Exencephaly and meroanencephaly
Microcephaly
Hydrocephalus
Holoprosencephaly
Mental retardation
اسم ورقم المقرر – Course Name and No.
7/13/2019

39. THE END