SECOND WEEKSECOND WEEK

Differentiation of the Differentiation of the embryo into three embryo into three germ layers : germ layers :

EctodermEctoderm. . MesodermMesoderm. . EndodermEndoderm.. The The EctodermEctoderm will will

formform (1) Central nervous (1) Central nervous

system.system. (2) Epidermis of Skin.(2) Epidermis of Skin.

THIRD WEEKTHIRD WEEK Neural Plate :Neural Plate : It is a dorsal midline It is a dorsal midline

thickening of the thickening of the ectoderm overlying ectoderm overlying the notochord the notochord ((NeuroectodermNeuroectoderm) .) .

THIRD WEEKTHIRD WEEK Neural Folds :Neural Folds : They are the elevated They are the elevated

lateral margins of the lateral margins of the neural plate.neural plate.

They are on each side They are on each side of the longtudinal of the longtudinal midline midline (Neural (Neural Groove).Groove).

NEURAL TUBENEURAL TUBE

It is formed from the It is formed from the apposition and apposition and fusion of the neural fusion of the neural folds which seal the folds which seal the neural groove and neural groove and create the tubecreate the tube..

FOURTH WEEKFOURTH WEEK

The neural tube is The neural tube is completed and completed and transformed into the transformed into the adult adult CNSCNS..

This growth is maximal at This growth is maximal at the rostral part which the rostral part which becomes the becomes the brainbrain..

The caudal portion The caudal portion becomes the becomes the spinal cordspinal cord..

The axis of the neural tube The axis of the neural tube (neuroaxis) is (neuroaxis) is straightstraight..

NEURAL GROOVENEURAL GROOVE

The central cavity The central cavity within the neural within the neural tube becomes :tube becomes :

VentriclesVentricles of the of the brain andbrain and

Central canalCentral canal of the of the spinal cord.spinal cord.

NEURAL CRESTNEURAL CRESTThey are separated cells They are separated cells

from the apices of the from the apices of the neural foldsneural folds..

They are dorsolateral to They are dorsolateral to the neural tubethe neural tube..

They give rise toThey give rise to: : Autonomic gangliaAutonomic ganglia..

Sensory gangliaSensory ganglia of spinal of spinal and cranial nervesand cranial nerves..

MelanocytesMelanocytes..Cells of Cells of supra renalsupra renal

medullamedulla..

DIFFERENTIATION OF DIFFERENTIATION OF SPINAL CORDSPINAL CORD

The The Grey matterGrey matter is located is located centrally around centrally around the central the central canal.canal.

The The White White mattermatter forms the forms the outer coat.outer coat.

DIFFERENTIATION OF DIFFERENTIATION OF SPINAL CORDSPINAL CORD

Sulcus LimitansSulcus Limitans : : It is a longtudinal It is a longtudinal

groove along the inner groove along the inner surface of the lateral surface of the lateral walls of the developing walls of the developing spinal cord. spinal cord.

It differentiates the It differentiates the grouping of cells (gray grouping of cells (gray matter) into dorsal matter) into dorsal (Alar)(Alar) plate and a plate and a ventral ventral (Basal) (Basal) plate.plate.

DIFFERENTIATION OF DIFFERENTIATION OF SPINAL CORDSPINAL CORD

The The AlarAlar plate is plate is predominantly predominantly sensory sensory in function.in function.

The The BasalBasal plate is plate is predominantly predominantly motormotor in function. in function.

DIFFERENTIATION OF BRAINDIFFERENTIATION OF BRAIN

55thth week week:: Three primary brain Three primary brain

vesicles appear :vesicles appear : Fore brain Fore brain

((ProsencephalonProsencephalon).). Mid brain Mid brain

((MesencephalonMesencephalon).). Hind brain Hind brain

((Rombencephalon).Rombencephalon).

FLEXURESFLEXURES

The neuraxis is The neuraxis is bent by two bent by two flexures :flexures :

CephalicCephalic ( Mid( Mid brain)brain) flexureflexure at at the junction of the junction of the fore and mid the fore and mid brains.brains.

Cervical flexureCervical flexure : : Between the brain Between the brain

and spinal cord.and spinal cord.

SEVENTH WEEKSEVENTH WEEK

FiveFive secondary secondary brain vesicles brain vesicles appear.appear.

PROSENCEPHALONPROSENCEPHALON

Is divided into :Is divided into : Telencephalon.Telencephalon. Diencephalon.Diencephalon.

TELENCEPHALONTELENCEPHALON

It is the largest It is the largest brain vesicle.brain vesicle.

It has the greatest It has the greatest degree of degree of development.development.

It forms the two It forms the two Cerebral Cerebral Hemispheres.Hemispheres.

DIENCEPHALONDIENCEPHALON

It is formed It is formed mainly of the mainly of the ThalamusThalamus..

The Thalamus The Thalamus contains contains numerous groups numerous groups of neurons and is of neurons and is connected with connected with the cerebral the cerebral cortex.cortex.

ROMBENCEPHALONROMBENCEPHALON

Is divided into :Is divided into : MetencephalonMetencephalon.. Mylencephalon.Mylencephalon.

PONTINE FLEXUREPONTINE FLEXURE

It is the third It is the third flexure that flexure that appears between appears between the the metencephalon metencephalon and the and the myelencephalon.myelencephalon.

METENCEPHALONMETENCEPHALON

It is It is differentiated differentiated into:into:

PonsPons . . Cerebellum.Cerebellum.

MYELENCEPHALONMYELENCEPHALON

It will form :It will form : The Medulla The Medulla

OblongataOblongata..

MESENCEPHALONMESENCEPHALON

It remains It remains undifferentiatedundifferentiated..

It is in the form of It is in the form of its embryonic its embryonic picturepicture: :

Central canal Central canal surrounded by surrounded by grey mattergrey matter..

BRAIN CENTERSBRAIN CENTERS They consist of : They consist of : Bilateral pairedBilateral paired

centers for the centers for the senses of : senses of :

SmellSmell, , Vision,Vision, Hearing Hearing and and

A symmetricalA symmetrical midlinemidline VestibularVestibular center for the center for the maintenance of maintenance of equilibrium.equilibrium.

BRAIN CENTERSBRAIN CENTERSThey start to They start to

appear as appear as expansions from expansions from the the dorsal aspectdorsal aspect of the simple of the simple tubular braintubular brain..

They are They are composed of an composed of an outer cortex of outer cortex of nerve cells with nerve cells with underlying core underlying core of nerve fibersof nerve fibers..

BRAIN CENTERSBRAIN CENTERS

The centers for vision The centers for vision and hearing will form and hearing will form largely automatic, largely automatic, reflex functions.reflex functions.

They are represented They are represented by the by the four colliculi four colliculi (superior & inferior).(superior & inferior).

The motor center The motor center near the caudal end near the caudal end of the brain will be in of the brain will be in the cerebellum.the cerebellum.

PROSENCEPHALISATIONPROSENCEPHALISATION The massive cerebral The massive cerebral

hemispheres which hemispheres which are developed from are developed from the the rostralrostral (olfactory) (olfactory) part of the brain take part of the brain take an executive role in an executive role in many functions of the many functions of the brain.brain.

PROSENCEPHALISATIONPROSENCEPHALISATION They become the They become the

highest levels for highest levels for perception and perception and correlation ofcorrelation of all all sensory modalitiessensory modalities

They are the highest They are the highest level for motor control.level for motor control.

The other centers The other centers become progressively become progressively subservient to the subservient to the cerebral hemispheres.cerebral hemispheres.

CONGENITAL ANOMALIESCONGENITAL ANOMALIES

(1) Anencephaly(1) Anencephaly The brain and The brain and

skull are minute.skull are minute. It is incompatible It is incompatible

for life. for life.

((22 ) )SPINA BIFIDASPINA BIFIDA

It is It is underdevelopmenunderdevelopment of the t of the lower lower part of the spinal part of the spinal cord and the cord and the nerve roots.nerve roots.

It may be It may be associated with associated with underdevelopmenunderdevelopment of the bone and t of the bone and skin.skin.

SPINA BIFIDASPINA BIFIDA

The infants with The infants with Spina Bifida Spina Bifida complain from :complain from :

Paralysed, Paralysed, anesthetic lower anesthetic lower limbs.limbs.

Incontinence of Incontinence of urine and stool.urine and stool.

((33 ) )MENINGIOMYELOCELEMENINGIOMYELOCELE

It is Spina Bifida It is Spina Bifida withwith

The appearance of The appearance of the meninges of the meninges of the spinal cord on the spinal cord on the back of the the back of the body.body.