Development of the Nervous System

Primary neurolation

Neural tube formation (aka brain)

First step to primary neurolation

Chemical signals in the 3rd week of embryonic development lead to formation of neural plates

nueral plate

A thickened portion of ectoderm

Second step to primary neurolation

Neural plate folds inward to form the neural groove in the midline with neural folds on each side

Third step to primary neurolation

At the beginning of the 4th week, neural folds fuse in midline to form neural tube

Fourth step to primary neurolation

Entire nueral is closed by end of 4th week in typical development

Fifth step to primary nuerolation

Nueral tube gives rise to entire CNS, cavity inside tube gives rise to ventricular system (in the brain) and central canal (spinal cord)

Sixth step to primary neurolation

As neural tube closes, it separates the ectoderm (skin) and leaves groups of nueral crest cells

nueral crest cells

Groups of cells from nueral folds that give rise to a variety of cell types including much of the PNS: dorsal root ganglia (sensory nuerons), autonomiic ganglia, adrena, medulla, some cranial nerves, etc

Secondary Neurulation

once neural tube closes, a secondary cavity forms into cells caudally during 5th and 6th weeks, this forms the sacral spinal cord region

suculus limitans

Longitudinal groove in wall of nueral tube in 4th week, separating the nueral tube and eventually the brain and spinal cord, into a dorsal half and ventral half

Alar plate

Dorsal to suculus limitans and has sensory functions

Basal plate

Ventral to suculus limitans and has motor functions

Prosencephalon (forebrain)

Primary vesicle, Forms the Telencephalon (becomes cerebrum) and Diencephalon.

Rhombencephalon (hindbrain)

Primary vesicle, forms metencephalon and myelencephalon

Mesencephalon (midbrain)

Primary vesicle of midbrain, remains as a secondary vesical

Telencephalon

Secondary vesicle derived from the prosencephalon, develops into cerebral hemispheres and contains the lateral ventricles

Diencephalon

Secondary vesicle derived from the prosencephalon, develops into the thalamus, hypothalamus, retina, etc, associated with the 3rd ventricle.

Mesencephalon (secondary vesicle)

Secondary vesicle derived from the prosencephalon, develops into the midbrain; associated with cerebral; aqueduct

Metencephalon

Secondary vesicle derived from the rhombencephalon; develops into the pons and cerebellum; forms part of the 4th ventricle.

Myelencephalon

Secondary vesicle derived from the rhombencephalon, becomes medulla oblongata, part of the 4th ventricle and central canal

cervical flexure

between future brainstem and spinal cord; straightens later in development

cephalic flexure

Future midbrain and diencephalon, persisting in adulthood and is the reason for the bend in the nueral axis

pontine flexure

between future pons and medulla; does not persist but affects caudal brainstem

growth of telencephalon

two swellings arise and fold over so that the telencephalon and diencephalon fuse, these swellings are the future cerebral hemispheres, viewed latterly diencephalon deep to telencephalon , curves into c shape