CNS DEVELOPMENTCNS DEVELOPMENT

Stages in Neural Tube Stages in Neural Tube DevelopmentDevelopment

Neural plate.Neural plate.

Neural folds.Neural folds.

Neural tube.Neural tube.

Time-LineTime-Line

Formation of nervous system occurs Formation of nervous system occurs during the embryonic stage:during the embryonic stage:

End of second week to end of eighth week.End of second week to end of eighth week.

Time-LineTime-Line

Superior (anterior or cranial) neuropore Superior (anterior or cranial) neuropore closes by day 27.closes by day 27.

Inferior (posterior or caudal) neuropore Inferior (posterior or caudal) neuropore closes by day 30.closes by day 30.

Subdivision of Cranial End of Subdivision of Cranial End of Neural TubeNeural Tube

Tripartite brain.Tripartite brain.

Pentapartite brain.Pentapartite brain.

Tripartite BrainTripartite Brain

Prosencephalon.Prosencephalon.

Mesencephalon.Mesencephalon.

Rhombencephalon.Rhombencephalon.

Pentapartite BrainPentapartite Brain

Prosencephalon:Prosencephalon:Telencephalon (most anterior).Telencephalon (most anterior).

Diencephalon.Diencephalon.Mesencephalon.Mesencephalon.Rhombencephalon:Rhombencephalon:

Metencephalon.Metencephalon.

Myelencephalon.Myelencephalon.

Telencephalon PrimordiaTelencephalon Primordia

Lumina:Lumina:Lateral ventricles (I, II).Lateral ventricles (I, II).

Floor:Floor:

Basal ganglia (nuclei).Basal ganglia (nuclei).

Olfactory lobes and nerves.Olfactory lobes and nerves.Roof:Roof:

Cerebral hemispheres.Cerebral hemispheres.

Diencephalon PrimordiaDiencephalon Primordia

Lumen:Lumen:Third ventricle.Third ventricle.

Roof:Roof:Epithalamus.Epithalamus.

Walls:Walls:Thalamus.Thalamus.

Floor:Floor:Hypothalamus and infundibulum.Hypothalamus and infundibulum.

Mesencephalon PrimordiaMesencephalon Primordia

Lumen:Lumen:Cerebral aqueduct (of Sylvius).Cerebral aqueduct (of Sylvius).

Roof =Tectum:Roof =Tectum:Superior and inferior colliculi.Superior and inferior colliculi.

Floor:Floor:Tegmentum.Tegmentum.

Metencephalon PrimordiaMetencephalon Primordia

Lumen:Lumen:Part of fourth ventricle.Part of fourth ventricle.

Roof:Roof:Cerebellum.Cerebellum.

Floor:Floor:Pons.Pons.

Myelencephalon PrimordiaMyelencephalon Primordia

Lumen:Lumen:Rest of fourth ventricle.Rest of fourth ventricle.

Main part:Main part:Medulla oblongata.Medulla oblongata.

Roof:Roof:Posterior choroid plexus.Posterior choroid plexus.

Histogenesis of Neural TubeHistogenesis of Neural Tube

Initial tube wall =Initial tube wall =Pseudostratified epithelium:Pseudostratified epithelium:

Single layer of cells, but cells are Single layer of cells, but cells are of of different different heights.heights.

All cells are in contact with a basement All cells are in contact with a basement membrane.membrane.

Outermost membrane =Outermost membrane =External limiting membrane.External limiting membrane.

Histogenesis of Neural TubeHistogenesis of Neural Tube

Some neuroepithelial cells remain Some neuroepithelial cells remain attached to the basement membrane and attached to the basement membrane and will form a single layer of ependymal cells will form a single layer of ependymal cells that will line the entire ventricular system that will line the entire ventricular system and the neural canal.and the neural canal.

Histogenesis of Neural TubeHistogenesis of Neural Tube

Tube differentiates into two concentric Tube differentiates into two concentric rings by day 26:rings by day 26:

Mantle layer and marginal layer.Mantle layer and marginal layer.

Histogenesis of Neural TubeHistogenesis of Neural Tube

Other cells lose contact with the basement Other cells lose contact with the basement membrane and will migrate past the ependymal membrane and will migrate past the ependymal cells to form a new outer layer of densely cells to form a new outer layer of densely packed cells collectively called the:packed cells collectively called the:

Mantle layer:Mantle layer: Cells that make up the mantle layer are:Cells that make up the mantle layer are:

NEUROBLASTS.NEUROBLASTS. Note that mantle layer is still covered by the Note that mantle layer is still covered by the

external limiting membrane.external limiting membrane.

Histogenesis of Neural TubeHistogenesis of Neural Tube Neuroblasts in the mantle layer will begin to Neuroblasts in the mantle layer will begin to

grow processes (axons) that will form a new grow processes (axons) that will form a new outer layer:outer layer:

Marginal layer.Marginal layer.The marginal layer is also located beneath The marginal layer is also located beneath the external limiting membrane.the external limiting membrane.

The marginal layer will form the white matter of The marginal layer will form the white matter of the spinal cord and the brain.the spinal cord and the brain.

The mantle layer forms the gray matter of the The mantle layer forms the gray matter of the brain and spinal cord (except for the cortices).brain and spinal cord (except for the cortices).

DEVELOPMENTAL DEVELOPMENTAL ANOMALIESANOMALIES

AnencephalyAnencephaly

Failure of cranial end of neural tube to Failure of cranial end of neural tube to close.close.

Arnold-Chiari deformityArnold-Chiari deformity

Inferior cerebellum and medulla are elongated Inferior cerebellum and medulla are elongated and protrude into vertebral canal.and protrude into vertebral canal.

Medulla and pons are small and deformed.Medulla and pons are small and deformed. Hydrocephalus.Hydrocephalus. Malformation of lower cranial nerves:Malformation of lower cranial nerves:

Deafness.Deafness.

Tongue, facial muscle, lateral eye Tongue, facial muscle, lateral eye movement movement weakness.weakness.

Spina Bifida OccultaSpina Bifida Occulta

Results from a failure of the inferior Results from a failure of the inferior neuropore to close.neuropore to close.

Vertebral arch(-es) fails to develop in Vertebral arch(-es) fails to develop in caudal area.caudal area.

Spinal cord function is usually normal.Spinal cord function is usually normal.

Spina Bifida CysticaSpina Bifida Cystica

Characterized by a sac-like cyst at the Characterized by a sac-like cyst at the caudal end of spine.caudal end of spine.

Spinal cord and/or meninges may be Spinal cord and/or meninges may be found in the cyst.found in the cyst.

Spinal cord function may be impaired.Spinal cord function may be impaired.May be lower extremity dysfunction.May be lower extremity dysfunction.Bladder and bowel function may be Bladder and bowel function may be

impaired.impaired.

MeningoceleMeningocele

Form of spina bifida cystica.Form of spina bifida cystica.Only meninges found in sac.Only meninges found in sac.Spinal cord function may be impaired.Spinal cord function may be impaired.Signs and symptoms vary depending on Signs and symptoms vary depending on

location and severity of malformation.location and severity of malformation.

MeningomyeloceleMeningomyelocele

Form of spina bifida cystica.Form of spina bifida cystica.Both meninges and spinal cord are found Both meninges and spinal cord are found

in sac.in sac.Always results in abnormal growth of Always results in abnormal growth of

spinal cord.spinal cord.Lower extremity paralysis.Lower extremity paralysis.Bowel and bladder dysfunction.Bowel and bladder dysfunction.Loss of sensation to lower limbs.Loss of sensation to lower limbs.

MyeloschisisMyeloschisis

Failure of caudal neural folds to close.Failure of caudal neural folds to close.Most severe of the defects.Most severe of the defects.

HoloprosencephalyHoloprosencephaly

Failure of prosencephalon to divide into Failure of prosencephalon to divide into two cerebral hemispheres.two cerebral hemispheres.

Often associated with facial deformities:Often associated with facial deformities:

Single orbit with two eyes or one eye or no Single orbit with two eyes or one eye or no eye.eye.

Proboscis-type nose located above eye.Proboscis-type nose located above eye.

Cleft lip and palate.Cleft lip and palate.