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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

THE END