5. The central nervous system (CNS) appears at
the beginning of the third week as a slippershaped
plate of thickenedectoderm, the
neural plate, in the mid-dorsal region in front of
the primitive node. Its lateral edges soon elevate
to form the neural folds
NEURAL FOLD
CUT EDGE OF AMNION
PRIMITIVE NODE
PRIMITIVE STREAK
SOMITE
NEURAL PLATE
NEURAL GROOVE
BA
FIGURE A. Dorsal view of a late presomite embryo at approximately 18 days. The amnion has been removed, and
the neural plate is clearly visible. B. Dorsal view at approximately 20 days. Note the somites and the neural grooveand
neural folds.
6. Neural folds form the neural tube and fusion of neural tube begins in
cranial to caudal direction
The cephalic end of the neural tube shows
three dilations, the primary brain vesicles:
(1) prosencephalon, or forebrain;
(2)mesencephalon, or midbrain; and
(3)rhombencephalon, or hindbrain
MIDBRAIN
FOREBRAIN
HINDBRAIN
Figure; Drawing of a sagittal section through thebrain at approximately 28 days of human development.Three
brain
vesicles represent the forebrain (F), midbrain(M), and hindbrain(H)
7. MESENCEOHALON
METENCEPHALON
ROOF OF 4TH VENTRICLE
MYELENCEPHALON
DIENCEPHALON
MESENCEPHALIC ISTHMUS
OPTIC VESICLE OUTPOCKETING
TELENCEPHALON
Figure 18.5 Drawing of a sagittal section through thebrain at approximately 32 days of human development.The threeoriginal brain
vesicles havesegregated into the telencephalon, diencephalon, mesencephalon, metencephalon, and
myelencephalon.
8. Prosencephalon: Forebrain
COMPRISES OF
> TELENCEPHALON – FORMS CEREBRAL HEMISPHERE
> DIENCEPHALON- FORMS optic cup
and stalk, pituitary, thalamus, hypothalamus, and
epiphysis
9. DIENCEPHALON
ROOF PLATE AND EPIPHYSIS
>Diencephalon develops from the median process of prosencephalon
And consist of one roof plate and two alar plates
> Roof plate consist of single layer of ependymal cells covered by vascular
mesenchyme
>Together they give rise to choroid plexus of third ventricle
>Most caudal part of roof plate forms Pineal Body or epiphysis
10. ALAR PLATE , THALAMUS AND HYPOTHALAMUS
> Forms lateral wall of diencephalon
> Hypothalamic sulcus or groove divides the plate into dorsal and ventral region
that is THALAMUS AND HYPOTHALAMUS RESPECTIVELY
> As a proliferativeactivity of thalamus , it gradually projects into lumen of
diencephalon
>This expansion is so
great that thalamicregions from the right and
left sides fuse in the midline, forming the massa
intermedia, or interthalamic connexus
> Hypothalamus forming lower portion of alar plates differentiate into number of
nuclear areas that regulate sleep , digestion, body temperature and emotional
behaviour
11. Choroid plexus
Hippocampus
Corpus
striatum
Foramen
of Monro
Lateral ventricle
Hypothalamus
Choroid
plexus
Pallium
Thalamus
3rd
ventricle
Mamillary body
Infundibulum
Hypothalamus
Lamina
terminalis
Optic
chiasma
Cerebral
hemisphere
Foramen
of Monro
Pineal
thickening
Roof plate of
diencephalon Epithalamus
Hypothalamic
sulcus
Figure
A. Medial surface of the right half of the prosencephalon in a 7-week embryo. B. Transversesection
through the prosencephalonat the level of the broken line in A. The corpus striatum bulges out in the fl oor of the lateral
ventricleand the foramen of Monro
A B
12. Hypothalamus OR Pituitary Gland
* Developsfrom
1) an ectodermal outpocketing of the stomodeum , immediately infront of oropharyngeal
membrane known as RATHKE'S POUCH
2) The downward extension of diencephalon , THE INFUNDIBULUM
* The anterior lobe of the hypophysisis formed from anterior wall of RATHKE'S POUCH
*A small extension of this lobe PARS TUBERALIS grows along the stalk of the infundibulumand infundibulum
* PARS INTERMEDIA develops from posterior wall of RATHKE'S pouch
* PARS NERVOSA developsfrom infundibulumand composed of NEUROGLIAL cells
13. Rathke's pouch
Infundibulum
NotochordOral
cavity
Anterior lobe
Pharyngeal
hypophysis
Sphenoid
bone
Optic chiasmaLumen of
diencephalon
Pars nervosa
Pars tuberalis
Pars intermedia
BA C
A. SAGITTAL SECTION THROUGH THE CEPHALIC PART OF 6TH WEEK EMBRYO SHOWING RATHKE'S POUCH AS A DORSAL OUTPOCKETTING OF THE
ORAL CAVITY AND INFUNDIBULUM AS A THICKENING OF THE FLOOR OF THE DIENCEPHLON
B,C. SAGITAL SECTION THROUGH THE HYPOPHYSIS IN THE 11TH AND 16TH WEEK OF DEVELOPMENT RESPECTIVELY. NOTE FORMATION OF PARS
TUBERALIS ENCIRCLING THE STALK OF THE PARS NERVOSA
14. TELENCEPHALON
Most rostral part of the brain vesicle and comprises of two lateral outpouching
THE CERBRAL HEMISPHERE AND
A MEDIAN PORTION LAMINA TERMINALIS
15. CEREBRAL HEMISPHERE
*Arises at the beginning of fifth week of developmt
* Bilateral invaginations of lateral wall of prosencephalon
*By the middle of the second month basal part of the hemisphere begin to grow and
bulge into the lumen of the lateral ventricle and into the floor of the foraminaof
MONRO
* In the region where wall of the hemisphere is attached to, the roof of the
diencephalon, the wall fails to develop neuroblasts and remain very thin
* Here , the hemisphere wall consist of the singlelayer of ependymal cells covered
by vascular mesenchyme and together they form choroid plexus
* Immediately above the choroid fissure the wall of the hemisphere thickens forming
the hippocampus. This structure’s
primary functionis olfaction, and it bulges into
the lateral ventricle
16. *Further expansion, the hemispheres cover the lateral aspect of the diencephalon, mesencephalon,
and cephalic portion of the metencephalon
* Corpus striatum expands posteriorly and is dividedinto two parts
1)Dorsomedial nucleus – caudate nucleus
2)Ventrolateral nucleus- lentiform nucleus
* this divisionis accomplishedby axons passing to and from the cortex of the hemisphere and breaking
through the nuclear mass of the corpus striatum. The fiber bundle thus formedis known as the internal
capsule
*Continuous growth of the cerebral hemispheres in anterior, dorsal, and inferior directions results in
the formation of frontal, temporal, and occipital lobes, respectively
17. Cortex Development
Develops from two regions
1) PALLEOPALLIUM OR ARCHIPALLEUM( IMMEDIATELLY LATERAL TO CORPUS STRIATUM)
2) NEOPALLIUM ( BETWEEN THE HIPPOCAMPUS AND THE PALEOPALLEUM)
*In the neopallium, waves of neuroblasts migrate to a subpial position and then differentiate
into fully mature neurons
*When the next wave of neuroblasts arrives, they migrate through the earlier-formedlayers of
cells until they reach the subpial position.
18. Mesencephalon: Midbrain
Each basal plate contains two groups of motor nuclei
General visceral
efferent group
Medial somatic
efferent group
represented by
the oculomotor and
trochlear nerves,
which
innervate the eye
musculature
represented
by the nucleus of
Edinger-Westphal,
which
innervates the
sphincter pupillary
muscle
19. CRUS CEREBRI- MARGINAL LAYER OF EACH BASAL PLATE ENLARGEMENT
These crura serve as pathways for nerve fibers descending from
the cerebral cortex to lower centers in the pons and spinal cord.
ALAR PLATE- Divides into anterior and posterior colliculus
ANTERIOR COLLICULUS - FUNCTIONS AS A CORRELATION
AND REFLEX CENTRE FOR VISUAL IMPULSES
POSTERIOR COLLICULUS - SYNAPTIC RELAY STATION FOR
AUDITORY REFLEXES
20. Rhombencephalon: Hindbrain
CONSIST OF
MYELENCEPHALON -most caudal of the brain vesicles
METENCEPHALON – Extends from pontine flexure to the
rhombencephalicisthmus
Myelencephalon
(medulla oblongata)
Mesencephalon
Cerebral
hemisphere
Cut edge of roof of
4th ventricle
Rhombencephalic
isthmus
Intraventricular
portion of
rhombic lip
diencephalon
FIG . Lateral view of the brain vesicles in an 8-
week embryo (crown-rump length ~27 mm).
21. MYELENCEPHALON
*Gives rise to medullaoblongata
*It differs from the spinal cord in that its lateral walls
are everted
*BASAL AND ALAR PLATES
BASAL PLATE – COMPRISE OF 3 NUCLEI
A. SOMATIC EFFERENT GROUP – FORMS CEPHALIC
CONTINUATION OF ANTERIOR HORN CELLS
- CONTAINS NEURONS OF HYPOGLOSSAL NERVE THAT
SUPPLY TONGUE MUSCULATURE
-In the metencephalon
and the mesencephalon, the column contains
neurons of the abducens (VI) ,
trochlear (IV), and oculomotor(III) nerves,
respectively.
22. IMAGEDESCRIPTION
Somatic afferent
MESENCEPHALON
TROCHLEAR NERVE
4TH
VENTRICLE
BASAL PLATE
RHOMBIC LIP
ATTACHMENT OF ROOF PLATE
ALAR PLATE
ALAR PLATE
ROOF PLATE
SULCUS LIMITANS
General
visceral efferent
BASAL PLATE
CHOROID PLEXUS
General
visceral afferent
Special visceral
afferent
Olivarynucleus
Somatic
efferent
(XII)
Special visceral
efferent
(IX, X, XI)
CA
B
A. Dorsal view of the fl oor of the fourth ventricle in a 6-week embryo after removal of the roof plate.
Note the alar and basal plates in the myelencephalon. The rhombic lip is visible in the metencephalon. B,C. Position and
differentiation of the basal and alar plates of the myelencephalon at different stages of development. Note formation of
the
nuclear groups in the basal and alar plates. Arrows, path followed by cells of the alar plate to the olivary nuclear complex.
The
choroid plexus produces cerebrospinal fl uid.
23. B. SPECIAL VISCERAL EFFERENT
-MOTOR NEURONS SUPPLY STRIATED MUSCLES OF PHARYNX
-Column is represented by neurons of the accessory (XI),
vagus (X), and glossopharyngeal (IX) nerves.
C. GENERAL VISCERAL EFFERENT
- Supply the involuntary musculature of respiratory tract, intestinal tract and
heart
ALAR PLATE – THREE GROUP OF SENSORY RELAY NUCLEI
A. GENERAL VISCERAL AFFERENT receives interoceptive information from the
gastrointestinal tract and heart
B. INTERMEDIATE SPECIAL AFFERENT impulses from taste buds of the tongue,
palate, oropharynx, and epiglottis and from the vestibulocochlear nerve (VIII) for
hearing and balance
C. LATERAL SOMATIC AFFERENT receives sensations of pain, temperature, and touch
from the pharynx by way of the glossopharyngeal nerve (IX)
24. *ROOF PLATE
Consists of a single layer of ependymal cells covered by vascular mesenchyme,the pia
mater. The two combinedare known as
the tela choroidea
* Because of active proliferation of vascular mesenchyme a number of sac like
invaginations projects into the ventricular cavity. These tuft like invaginations from
choroid plexus produce CSF
25. METENCEPHALON
CHARACTERISED BY BASAL AND ALAR PLATES.
TWO NEW COMPONENTS FORM
1) CEREBELLUM Coordinationcentre for posture abd movement
2) PONS pathway for nerve fibres between spinal cord and cerebral
and cerebellar cortices
BASAL PLATE OF METENCEPHALON CONTAINS THREE GROUPS OF
MOTOR NEURONS
A. MEDIAL SOMATIC EFFERENT - Giverise to nucleus of 6th nerve
B. SPECIAL VISCERAL EFFERENT- Contains nuclei of trigeminal and facial
nerve and innervates muscleof 1st and 2nd pharyngeal arch
C. GENERAL VISCERAL EFFERENT – supply submandibular and sublingual
salivary gland
26. ALAR PLATE – THREE SENSORY NUCLEI
A. LATERAL SOMATIC AFFERENT GROUP CONTAIN NEURON OF TRIGEMINAL NERVE
B. SPECIAL AFFERENT GROUP
C. GENERAL VISCERAL AFFERENT GROUP
The marginal layer of the basal plates of the
metencephalonexpands as it makes a bridge
for nerve fibers connecting the cerebral cortex
and cerebellar cortex with the spinal cord.
Hence, this portion of the metencephalonis
known as the pons (bridge).
27. CEREBELLUM
*The dorsolateral parts of the alar plates bend mediallyand form the rhombic lips
*Rhombiclips compress cephalocaudally and form the cerebellar plate
*In a 12-week embryo, this plate shows a small midline portion, the vermis, and two lateral
portions, the hemispheres
*The transverse fi ssure soon separates the nodule from the vermis and the lateral fl
occulus from the hemispheres
*The cerebellar plate consists of
neuroepithelial, mantle, and marginal layers
*Number of cells formed by the neuroepithelium migrate to the surface of the cerebellum
to form the external granular layer.
*Cells of this layer retain their ability to divide and form a proliferative
zone on the surface of the cerebellum
* in sixth month of development these cells gives rise to a) granule cell b)basket cell
c)stellate cell
*The cortex of the cerebellum,consisting of Purkinje cells, Golgi II neurons, and neurons
produced by the external granular layer, reaches its definitive size after birth
*dentate nucleus, reach their final position before birth
28. COMMISURES
-The first of the crossing bundles to appear is the anterior commissure
-Consists of fibers connecting the olfactory bulb and related brain areas of
one hemisphere to those of the opposite side
-The second commissure to appear is the
hippocampal commissure, or fornix commissure
- Fibers arise in the hippocampus
and converge on the laminaterminalis close to
the roof plate of the diencephalon
-Most important commissure is the corpus callosum. It appears by the 10th
week of development and connects the nonolfactory areas of the right and
the left cerebral cortices
-Posterior and habenular
commissures, are just below and rostral to thestalk of the pineal gland. The
third, the opticchiasma, which appears in the rostral wall of the
diencephalon, contains fibers from the medial halves of the retinae
