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CNS DEVELOPMENT
Stages in Neural Tube
Development

Neural plate.

Neural folds.

Neural tube.
Time-Line

Formation of nervous system occurs
during the embryonic stage:
End of second week to end of eighth week.
Time-Line

Superior (anterior or cranial) neuropore
closes by day 27.

Inferior (posterior or caudal) neuropore
closes by day 30.
Subdivision of Cranial End of
Neural Tube

Tripartite brain.

Pentapartite brain.
Tripartite Brain

Prosencephalon.

Mesencephalon.

Rhombencephalon.
Pentapartite Brain

Prosencephalon:
Telencephalon (most anterior).
Diencephalon.
Mesencephalon.
 Rhombencephalon:

Metencephalon.
Myelencephalon.
Telencephalon Primordia

Lumina:
Lateral ventricles (I, II).

Floor:
Basal ganglia (nuclei).
Olfactory lobes and nerves.

Roof:
Cerebral hemispheres.
Diencephalon Primordia

Lumen:
Third ventricle.

Roof:
Epithalamus.

Walls:
Thalamus.

Floor:
Hypothalamus and infundibulum.
Mesencephalon Primordia

Lumen:
Cerebral aqueduct (of Sylvius).

Roof =Tectum:
Superior and inferior colliculi.

Floor:
Tegmentum.
Metencephalon Primordia

Lumen:
Part of fourth ventricle.

Roof:
Cerebellum.

Floor:
Pons.
Myelencephalon Primordia

Lumen:
Rest of fourth ventricle.

Main part:
Medulla oblongata.

Roof:
Posterior choroid plexus.
Histogenesis of Neural Tube

Initial tube wall =
Pseudostratified epithelium:
Single layer of cells, but cells are of different
heights.
All cells are in contact with a basement
membrane.

Outermost membrane =
External limiting membrane.
Histogenesis of Neural Tube

Some neuroepithelial cells remain
attached to the basement membrane and
will form a single layer of ependymal cells
that will line the entire ventricular system
and the neural canal.
Histogenesis of Neural Tube

Tube differentiates into two concentric
rings by day 26:
Mantle layer and marginal layer.
Histogenesis of Neural Tube



Other cells lose contact with the basement
membrane and will migrate past the ependymal
cells to form a new outer layer of densely
packed cells collectively called the:
Mantle layer:
Cells that make up the mantle layer are:
NEUROBLASTS.
Note that mantle layer is still covered by the
external limiting membrane.
Histogenesis of Neural Tube



Neuroblasts in the mantle layer will begin to
grow processes (axons) that will form a new
outer layer:
Marginal layer.
The marginal layer is also located beneath
the external limiting membrane.
The marginal layer will form the white matter of
the spinal cord and the brain.
The mantle layer forms the gray matter of the
brain and spinal cord (except for the cortices).
DEVELOPMENTAL
ANOMALIES
Anencephaly

Failure of cranial end of neural tube to
close.
Arnold-Chiari deformity




Inferior cerebellum and medulla are elongated
and protrude into vertebral canal.
Medulla and pons are small and deformed.
Hydrocephalus.
Malformation of lower cranial nerves:
Deafness.
Tongue, facial muscle, lateral eye movement
weakness.
Spina Bifida Occulta

Results from a failure of the inferior
neuropore to close.

Vertebral arch(-es) fails to develop in
caudal area.

Spinal cord function is usually normal.
Spina Bifida Cystica
Characterized by a sac-like cyst at the
caudal end of spine.
 Spinal cord and/or meninges may be
found in the cyst.
 Spinal cord function may be impaired.
 May be lower extremity dysfunction.
 Bladder and bowel function may be
impaired.

Meningocele
Form of spina bifida cystica.
 Only meninges found in sac.
 Spinal cord function may be impaired.
 Signs and symptoms vary depending on
location and severity of malformation.

Meningomyelocele
Form of spina bifida cystica.
 Both meninges and spinal cord are found
in sac.
 Always results in abnormal growth of
spinal cord.
 Lower extremity paralysis.
 Bowel and bladder dysfunction.
 Loss of sensation to lower limbs.

Myeloschisis
Failure of caudal neural folds to close.
 Most severe of the defects.

Holoprosencephaly
Failure of prosencephalon to divide into
two cerebral hemispheres.
 Often associated with facial deformities:

Single orbit with two eyes or one eye or no
eye.
Proboscis-type nose located above eye.
Cleft lip and palate.