DR SHABANA ALI

Three primordial

tissues

endoderm

mesoderm

ectoderm

Which tissue does

nervous system

develop from?

ectoderm

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appears at the beginning of the 3rd week as a

slipper-shaped plate of thickened ectoderm,

the neural plate.

Its lateral edges soon elevate to form neural

Folds.

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Neural

crest

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The neural folds approach each other in the

midline,forming neural tube .

begins in the cervical region and proceeds in

cephalic and caudal directions.

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Neural

crest

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Anterior

neural

pore

Posterior

neural

pore

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Closure of the cranial

neuropore occurs at the25th

day

Closure of the caudal

neuropore occurs at 27 day.

Anterior

neural

pore

Posterior

neural

pore

failure to close =

anencephaly

failure to close =

spina bifida

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Neural crest becomes

peripheral nervous

system (PNS)

Neural tube becomes

central nervous system

(CNS)

Somites become spinal

vertebrae.

Somites

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Prosencephalon

or forebrain

Mesencephalon

or midbrain

Rhombencephalon

or hindbrain

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mesencephalon

metencephalon

myelencephalon

6 weeks4 weeks

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Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 48.20

THE TELENCEPHALON, which forms the

cerebral hemispheres.

THE DIENCEPHALON, which forms the optic

cup and stalk,pituitary gland , thalamus,

hypothalamus, and epiphysis.

The diencephalon, consist of a roof plate

and two alar plates but there are no floor

and basal plates

a single layer of ependymal cells with

vascular mesenchyme give rise to the

choroid plexus of the third ventricle .

The most caudal part of the roof plate

develops into the pineal body, or epiphysis.

serves as a channel through which light and

darkness affect endocrine and behavioral

rhythms.

lateral walls of the diencephalon.

the hypothalamic sulcus, divides the plate

into a dorsal and a ventral region, the

thalamus and hypothalamus,

As a result of proliferative activity, the

thalamus gradually projects into the lumen

of the diencephalon,forming the massa

intermedia, or interthalamic connexus.

The telencephalon, the most rostral of the

brain vesicles, consists of

two lateral outpocketings, the cerebral

hemispheres

a median portion, the lamina terminales.

The cavities of the hemispheres, the lateral

ventricles, communicate with the lumen of

the diencephalon through the

interventricular foramina of Monro

arise at the beginning of the fifth week of

development as bilateral evaginations of the

lateral wall of the prosencephalon.

By the middle of the second month the basal

part of the hemispheres begins to grow and

bulges, has a striated appearance and is

known as the corpus striatum .

Near the diencephlon a single layer of ependymal

cells covered by vascular mesenchyme form the

choroid plexus.

Immediately above the choroidal fissure, the

wall of the hemisphere thickens, forming the

hippocampus.

With further expansion, the hemispheres

cover the lateral aspect of the diencephalon,

mesencephalon, and cephalic portion of the

metencephalon

internal capsule divide nuclear mass of the

corpus striatum by axons passing to and from

the cortex of the hemisphere.

At the same time, the medial wall of the

area between the frontal and temporal lobes

becomes depressed and is known as the

insula .

During the final part of fetal life, the surface

of the cerebral hemispheres grows so rapidly

that a great many convolutions (gyri)

separated by fissures and sulci appear on

its surface

Cortex Development.

The cerebral cortex develops from the

pallium, which has two regions:

(a) the paleopallium, or archipallium,

immediately lateral to the corpus striatum,

(b) the neopallium,between the

hippocampus and the paleopallium

a number of fiber bundles, cross the

midline, connect the right and left halves of

the hemispheres.

The most important fiber bundles make use

of the lamina terminalis.

anterior commissure.

hippocampal commissure, or

fornix commissure.

corpus callosum.

posterior and habenular commissures,

the optic chiasma

Holoprosencephaly

Exencephaly

Hydrocephalus

Microcephaly

1.Mylencephlon ----medulla oblangata

Basal plate-------- three motor nuclei

Alar plate----------three sensory nuclei

Roof plate------ ---ependymal layer(choroid

plexus)

Floor plate---------region of median sulcus

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Metencephlon -----cerebellum,pons .

Basal plate----------three motor nuclei

Marginal zone of basal plate---pons

Alar plate-----------pontine nuclei,three

sensory nuclei

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Basal plate ; 2 groups of efferent nuclei

Marginal layer- --------- crus cerebri

Alar plate---------------superior and inferior

colliculi

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THE TELENCEPHALON, which forms the

cerebral hemispheres.

THE DIENCEPHALON, which forms the optic

cup and stalk,pituitary gland , thalamus,

hypothalamus, and epiphysis.