1. Development of the CNS
Normal and Abnormal

2. Lectures Objectives
Describe the formation of neural tube and neural crest.
Describe the development of brain and spinal cord.
Describe the positional changes of spinal cord.
Describe the development of the spinal nerves and their spinal ganglia.
Describe the development of meninges.
Describe the development of brain vesicles from the neural tube.
Describe the development of the different parts of brain.
Describe the development of brain ventricles and choroid plexuses.
Describe the development of the cranial nerves and their ganglia.
Describe the congenital anomalies of brain and spinal cord.

3. Neurulation
The notochord induces the ectodermal cells over it to form the neural plate
Neural plate  the neural folds and neural groove that will fuse to form the neural tube (the primordium of the CNS)

4. Neurulation…
Neural tube forms and separate from the above ectoderm (the primordium of epidermis)in the third week
During the neural tube formation cells on the crest of the neural folds (neural crest) migrate laterally
Neural crest cells form the ganglia in the PNS and other tissues

5. Development of NS Neural plate forms the nervous system
Neural tube forms the CNS
Neural crest forms the PNS and ANS
Neural canal becomes the ventricles and spinal canal

6. Contribution of the Neural Crest
Derived from neuroectoderm
Give rise to or participate in the formation of many cells types and organs:
Sensory neurons of the spinal nerves, cranial nerves (V, VII, IX, and X)
Autonomic ganglia
Sheathing cells of the peripheral nervous system
Pigment cells of the dermis
Muscles, connective tissues, and bones of pharyngeal arch origin
Suprarenal medulla
Meninges (coverings) of the brain and spinal cord

8. Development of NS By the end of the 4th week
Rostral neuropore closed and forebrain develop
Caudal neuropore closed and caudal eminence develop

9. Development of the Spinal Cord
Neural tube caudal to the 4th somites forms SC
Thickening of the neural tube forming three layers
Ependymal (ventricular) layer
Mantle layer
Marginal Layer

10. Histogenesis of the Neural Tube
Ependymal (ventricular) layer → blast cells (migrate to mantle layer)
– Remaining cells → ependymal cells
Microglia – from bone marrow
Mantle layer → cells of CNS
Neuroblasts
Motor neurons (somatic & Autonomic)
Interneurons
Gliablasts (invade both mantle and marginal layers)
Astrocytes
Oligodendrocytes
Marginal Layer – white mater

11. Regions of the Spinal Cord
Ependyma
Marginal layer
Roof and floor plates
Sulcus limitans
Mantle layer
Alar plates – dorsal gray columns
sensory input
Internuncials, Commissurals, Tract fibers
Thickening forms dorsal septum
Basal plates – ventral gray columns
Somatic & visceral motor neurons
Thickening forms ventral median fissure

12. Neural Tube Defects
Spina bifida: results from failure of the neural tube to close in the vertebral column

13. Spina Bifida Spina bifida occulta Spina bifida cystica
Defect in vertebral arch
– L5‐S1
No clinical symptoms
Spina bifida cystica
With meningocele
1/1000
Sac contains meninges & CSF
With meningomyelocele
2‐4/1000
Sac contains spinal cord and/or nerves
Neurological deficits

14. Development of the Brain: Vesicles

15. Brain Flexures Happens due to the rapid growth of the brain
Midbrain flexure
Ventrally
Cervical flexure
Between hindbrain & SC
Pontine flexure
Between metencephalon & myelencephalon
Dorsally

16. Myelencephalon Caudal part Rostral part Closed part (spinal canal)
Neuroblasts from alar plates migrate into the marginal zone
Gracile & cuneate nuclei
Pyramids – ventrally
Rostral part
Open part
Lateral plates diverts away & roof plate widens
Alar plates lateral
» Afferent neurons
» Olivary nuclei
Basal plates medial
» Efferent nuclei

17. Myelencephalon Functional components of cranial nerves Basal plates
GSE – IIX nerve
SVE – IX nerve
GVE – X, XI nerves
Sulcus limitans
Alar plates
GVA
SVA
GSA
SSA
This order is valid for entire brainstem

18. Metencephalon Walls → pons & cerebellum
Cavity → rostral part of 4th ventricle
Alar plates gives rise to cerebellar swellings
Cerebellar swelling fuse in the midline
Neuroblasts from alar plates forms
Cerebellar cortex
Central nuclei of cerebellum
Pontine nuclei (cochlear & vestibular nuclei)
Sensory nuclei of trigeminal nerve

19. Midbrain Neural canal → cerebral aqueduct Alar plates Basal plates
Tectum nuclei
Superior & inferior colliculi
Basal plates
Tegmentum nuclei
III, IV nerves
Red nucleus
Substantia nigra

20. Diencephalon Three swelling from the lateral wall of the 3rd ventricle
– Epithalamus
Epithalamic sulcus
– Thalamus
Hypothalamic sulcus
– Hypothalamus

21. Telencephalon Cerebral vesicles → cerebral hemispheres
Enlarge and becomes C‐ shape
Caudal end enlarge and fold – temporal lobe
Cavity → anterior part of 3rd ventricle & lateral ventricles (c‐shape)
Temporal horn follow temporal lobe

22. Telencephalon
Corpus striatum develops from swelling in the floor of each cerebral hemisphere
– Fibers (C‐shape internal capsule) divide it into C‐ shape caudate nucleus & lentiform nucleus
Neuroblast cells migrate to marginal zone to form cerebral cortex

23. Telencephalon Cerebral commissures Lamina terminalis
Anterior commissure
Hippocampal commissure (fornix)
Corpus callosum
Begins at lamina terminalis and grows beyond it
Septum pellucidum
Between fornix & corpus callosum
Optic chiasm

24. Telencephalon Growth of the cerebral hemispheres results in
The development of sulci and gyri
The hidden insula

25. Congenital Anomalies of the Brain

26. Defective Closure of Rostral Neuropore
Anencephaly
Meroanencephaly
– 1/1000
Cranium bifidium
1/2000
Mostly in mid‐occipital
Cranial meningocele
Meningoencephalocele
meningohydroencephalocele

27. Hydrocephalus
Blockage of drainage of CSF (tumor, inflammation, developmental malformation, meningitis, hemorrhage or injury)
Continued production cause an increase in pressure ‐‐‐ hydrocephalus
In newborn or fetus, the fontanels allow this internal pressure to cause expansion of the skull and damage to the brain tissue
Neurosurgeon implants a drain shunting the CSF to the veins of the neck or the abdomen

28. Development of the Spinal Nerves
Motor nerve fibers
Begin to appear in the fourth week,
Arising from nerve cell in basal plates
Form ventral nerve roots
Sensory fibers form dorsal root
Originate from nerve cells in
spinal ganglia
Derived from neural crest cells
Proximal grow into the dorsal horns
Distal processes join the ventral nerve roots to form a spinal nerve

29. Development of the Spinal Nerves
Spinal nerves divide into dorsal and ventral primary rami
Contain both motor and sensory fibers
Dorsal rami innervate the back (muscles, vertebral joints, and skin)
Ventral rami innervate the limbs and ventral body wall
Form nerve plexuses

30. Differential Growth Changes the Position of the Spinal Cord with Respect to the Vertebral Column
3rd Month
5th Month
Newborn