CNS Development
- 2. Learning objectives • Neural tube formation, neural crest cells origin; • Brain development • Spinal cord development • Meningeal development • Pituitary gland development
- 3. Stages of Embryonic development
- 4. Neurulation Neural Tube • The nervous system develops when the notochord induces its overlying ectoderm to become neuroectoderm and • This now develop into the neural plate. • The neural plate folds along its central axis to form a neural groove • lined on each side by a neural fold
- 5. • The two neural folds fuse together and pinch off to become the neural tube. • Fusion of the neural folds begins in the middle of the embryo and moves cranially and caudally. • The cranial open end of the tube is the anterior (rostral) neuropore, and • the caudal open end of the tube is the posterior (caudal) neuropore. • The anterior neuropore closes on or before day 26 and • the caudal neuropore closes before the end of the fourth week.
- 6. Neural Crest • Some cells from the neural folds give rise to pleuripotent neural crest cells, • they migrate widely in the embryo to give rise to many nervous structures: • · Spinal ganglia (dorsal root ganglia) • · Ganglia of the autonomic nervous system • · Ganglia of some cranial nerves • · Sheaths of peripheral nerves • · Meninges of brain and spinal cord • · Pigment cells • · Suprarenal medulla • · Skeletal and muscular components in the head
- 7. Summary: Embryonic Development • Nervous system develops from ectoderm – by 3rd week, neural plate becomes a groove with neural folds along each side – by 4th week, neural folds join to form neural tube – lumen of the neural tube develops into central canal of spinal cord & ventricles of the brain – cells along the margin of the neural groove is called the neural crest • develop into sensory and sympathetic neurons & schwann cells – NB: By 4th week, neural tube exhibits 3 anterior dilations
- 8. Stages of Embryonic development
- 9. Brain Development • 4th week – forebrain – midbrain – hindbrain • 5th week – telencephalon – diencephalon – mesencephalon – metencephalon – myelencephalon
- 10. Brain development • By wk 4, the neural tube forms three primary brain vesicles. • The primary brain vesicles give rise to five secondary brain vesicles, • which give rise to the various adult structures.
- 13. Week 5 brain stage development
- 14. Primary vesicles Secondary vesicles Adult structures Forebrain vesicle (prosencephalon) Telencephalon Cerebral hemispheres, consisting of the cortex and medullary center, basal ganglia, lamina terminalis, hippocampus, the corpus striatum, and the olfactory system Diencephalon Thalamus, epithalamus, hypothalamus, subthalamus, neurohypophysis, pineal gland, retina, optic nerve, mamillary bodies Midbrain vesicle (mesencephalon) Mesencephalon Midbrain Hindbrain vesicle (rhombencephalon) Metencephalon Pons and cerebellum Myelencephalon Medulla
- 15. Ventricular System (Cerebrospinal Fluid System) • Fluid filled cavities found within the developing brain system originate from lumen of the developing neural tube • 5 cavities- lateral vent-1 pair • -3rd vent • -4th vent • Lined by choroid plexus made of ependymal cells-BBB
- 16. Ventricles in forebrain • Lateral ventricles-one pair • Ventricles in brainstem: • Mesencephalon 3rd /cerebral aqueduct • Metencephalon 4th ventricle • Mylencephalon 4th ventricle
- 17. Ventricular communication in the brain • Lateral-3rd vent foramen of Monro • 3rd to 4th vent cerebral aqueduct of sylvius • 4th to lateral aperture foramen of luschka • 4th to median aperture foramen of mengedie
- 18. Lateral view
- 19. Superior view
- 20. Anterior view
- 21. vermis Occipital LobeThalamus Corpus callosum Hypothalamus Fornix Anterior commissure Optic nerve 4th ventricle Posterior commissure pyramid Mammillary body Quadrigeminal cistern
- 22. Medial view
- 23. Development of Spinal Cord • The neural tube consists of three cellular layers from inner to outer: • the ventricular zone (ependymal layer), • the intermediate zone (mantle layer), and • the marginal zone (marginal layer).
- 24. ventricular zone • The ventricular zone gives rise to neuroblasts (future nerve cells) and • glioblasts (future supporting cells), which migrate into the intermediate zone to form two collections of cells (the alar plate and the basal plate) • separated by a groove called the sulcus limitans.
- 25. Alar and basal plate cells • Cells in the alar plate become afferent (sensory) neurons and • form the dorsal (posterior) horn of the spinal cord. • Cells in the basal plate become efferent (motor) neurons and • form the ventral (anterior) horn of the spinal cord. • The two ventral horns bulge ventrally to create a ventral median fissure. • While, the dorsal horns merge to create the dorsal median septum. • The lumen of the neural tube becomes the central canal of the spinal cord.
- 26. • The spinal cord extends throughout the entire length of the vertebral canal at week 8 of development. • At birth, the conus medullaris extends to the L3 vertebra. • In the adult, the conus medullaris extends to the L1 vertebra. • NB: Spinal lumbar punctures procedure must be performed caudally to the conus medullaris to avoid damaging the spinal cord.
- 27. Development of Meninges • The dura mater arises from paraxial mesoderm that surrounds the neural tube. • While, both the pia mater and arachnoid mater arise from neural crest cells.
- 28. Hypophysis (Pituitary Gland) • The anterior pituitary gland (adeno- hypophysis) arises from an evagination of the oropharyngeal membrane known as Rathke’s pouch. • The posterior pituitary gland (neuro- hypophysis) arises from an evagination of neuroectoderm from the diencephalon.
- 29. Clinical Correlations of spinal cord lesions • Spina Bifida • · Spina bifida occulta is a defect of the vertebral column only, and is a common problem affecting as many as 10% of live births.( NB: normal afeto- protein) • · Spina bifida with meningocele (spina bifida cystica) is a defect of the vertebral column with protrusion of the meninges through the defect. • · Spina bifida with myelomeningocele is a defect of the vertebral column protrusion of the meninges and herniation of the spinal cord through the defect.
- 30. • · Spina bifida with myeloschisis results from the failure of the caudal neuropore to close at the end of the fourth week of development. -- Newborn infants are paralyzed distal to the lesion. • These defects usually occur in the cervical and/or lumbar regions and may cause neurologic deficits in the lower limbs and urinary bladder. • Neural tube defects can be detected by the presence of alpha-fetoprotein (AFP) in the fetal circulation after the fourth week of development.
- 31. Anormalies of the brain • Anencephaly • Anencephaly is the failure of the anterior neuropore to close, resulting in a failure of the brain to develop. • Microcephaly • Microcephaly (small head) results from microencephaly (small brain), or the failure of the brain to grow normally. • This can be the result of exposure to large doses of radiation up to the sixteenth week of development, or from certain infectious agents (cytomegalovirus, herpes simplex virus, and toxoplasma gondii- TORCHES)
- 32. Applied anatomy of CNS • Hydrocephalus • Hydrocephalus is an accumulation of CSF in the ventricles of the brain, caused most commonly by stenosis of the cerebral aqueduct. In the absence of surgical treatment in extreme cases the head may swell to three times its normal size. • Arnold-Chiari Malformation • Arnold-Chiari malformation is herniation parts of the cerebellum (medulla oblongata and cerebellar vermis) through the foramen magnum of the skull. • Fetal Alcohol Syndrome • Ingestion of alcohol during pregnancy is the most common cause of infant mental retardation. It also causes microcephaly and congenital heart disease.