development of brain

DEVELOPMENT OF BRAIN

BRAIN VESICLES &FLEXURES

BRAIN VESICLES

• PRIMARY VESICLES APPEAR DURING THE 4th WEEK

• SECONDARY VESICLES APPEAR DURING THE 5th WEEK

BRAIN FLEXURES

• 1 MIDBRAIN FLEXURE IN THE MIDBRAIN REGION

• 2 CERVICAL FLEXURE B/W THE HINDBRAIN AND SP CORD—AT THE LEVEL OF SUPERIOR ROOT OF C1

• 3 PONTINE FLEXURE PRODUCED AS A RESULT OF UNEQUAL GROWTH OF BRAIN B/W 1 & 2 IT IS IN THE OPPOSITE DIRECTION –RESULTS IN THE THINNING OF THE ROOF OF HINDBRAIN

BRAIN FLEXURES

• PRODUCE VARIATIONS IN THE OUTLINE OF TRANSVERSE SECTIONS AT DIFFERENT LEVELS OF THE BRAIN AND IN THE POSITIONS OF GRAY AND WHITE MATER

• SULCUS LIMITANS EXTENDS CRANIALLY TO THE JUNCTION OF MIDBRAIN AND FOREBRAIN

• ALAR AND BASAL PLATES ARE RECOGNIZABLE ONLY IN THE HINDBRAIN AND MIDBRAIN

DEVELOPMENTOF HINDBRAIN [RHOMBENCEPHALON ]

• MYELENCEPHALON [MEDULLA OBLONGATA ]• CAUDAL /CLOSED PART • ROSTRAL/OPEN PART• CAUDAL PART• RESEMBLES SP CORD DEVELOPMENTALLY AND

STRUCTURALLY• LUMEN FORMS A SMALL CENTRAL CANAL

DEVELOPMENT OF MEDULLA OBLONGATA

• ROSTRAL PART• WIDE AND FLAT OPPOSITE THE PONTINE

FLEXURE• PONTINE FLEXURE CAUSES LATERAL WALLS OF

THE MEDULLA TO MOVE OUTWARD LIKE THE PAGES OF AN OPEN BOOK

• ROOF PLATE IS ALSO THINNED AND GREATLY STRETCHED

• NEUROBLASTS IN THE BASAL PLATE• ORGANIZE INTO THREE COLMNS ON EACH SIDE---

FROM MEDIAL TO LATERAL• 1 GENERAL SOMATIC EFFERENT—NEURONS OF

HYPOGLOSSAL NERVE• 2 SPECIAL VISCERAL EFFERENT---NEURONS

INNERVATING MUSCLES DERIVED FROM PHARYNGEAL ARCHES

• 3 GENERAL VISCERAL EFFERENTS ---SOME NEURONS OF GLOSSOPHARYNGEAL AND VAGUS NERVE

DEVELOPMENT OF MEDULLA


• NEUROBLASTS IN THE ALAR PLATE• FORM NEURONS THAT ARE ARRANGED IN FOUR

COLUMNS ON EACH SIDE FROM MEDIAL TO LATERAL

• 1 GENERAL VISCERAL AFFERENT---RECEIVE IMPULSES FROM

• 2 SPECIAL VISCERAL AFFERENT---RECEIVE TASTE FIBRES

• 3 GENERAL SOMATIC AFFERENT---RECEIVE IMPULSES FROM THE SURFACE OF THE HEAD


• NEUROBLASTS IN THE ALAR PLATE [CONTD ]• 4 SPECIAL SOMATIC AFFERENT---RECEIVE

IMPULSES FROM THE EAR

• SOME NEUROBLASTS FROM ALAR PLATE MIGRATE VENTRALLY AND FORM NEURONS IN THE OLIVARY NUCLEUS

•DEVELOPMENT OF PONS

• RHOMBENCEPHALON CONSISTS OF—

• MYELENCEPHALON –MEDULLA OBLONGATA • METENCEPHALON—PONS • ---CEREBELLUM• CAVITY OF THE METANCEPHALON FORMS THE

UPPER PART OF 4th VENTRICLE

DEVELOPMENT OF PONS

• ARISES FROM THE ANTERIOR PART OF METANCEPHALON

• ALSO RECEIVES CELLULAR CONTRIBUTIONS FROM ALAR PART OF MYELENCEPHALON

• PONTINE FLEXURE CAUSES DIVERGENCE OF LATERAL WALLS OF PONS AND SPREADS GRAY MATER IN THE FLOOR OF 4th VENTRICLE

• NEUROBLASTS IN EACH BASAL PLATE DEVELOP INTO MOTOR NUCLEI AND ORGANIZE INTO 3 CLUMNS ON EACH SIDE

DEVELOPMENT OF PONS

• NEURONS OF BASAL PLATES FORM THE MOTOR NUCLEI OF CRANIAL NERVES 5,6 & 7

• NEURONS OF VENTROMEDIAL PART OF EACH ALAR PLATE FORM THE

• 1 MAIN SENSORY NUCLEUS OF CR N 5• SENSORY NUCLEUS OF CR N 7• VESTIBULAR NUCLEUS OF CR N 8• COCHLEAR NUCLEUS OF CR N 8• PONTINE NUCLEI

DEVELOPMENT OF PONS

• AXONS OF PONTINE NUCLEI GROW TRANSVERSELY AND ENTER THE DEVELOPING CEREBELLUM OF THE OPPOSITE SIDE TO FORM THE TRANSVERSE PONTINE FIBRES AND MIDDLE CEREBELLAR PEDUNCLE

DEVELOPMENT OF CEREBELLUM

• DEVELOPS FROM THE POSTERIOR PART OF ALAR PLATES OF METENCEPHALON

• ON EACH SIDE THE ALAR PLATES BEND MEDIALLY TO FORM THE RHOMBIC LIP

• IN THE CAUDAL PART OF THE METANCEPHALON THE RHOMBIC LIPS ARE WIDELY SEPARATED

• IMMEDIATELY BELOW THE MESENCEPHALON THEY APPROACH EACH OTHER IN THE MIDLINE


• PONTINE FLEXURE DEEPENS• RHOMBIC LIPS COMPRESS TO FORM THE

CEREBELLAR PLATES• PLATES FUSE IN THE MIDLINE• DURING FUSION THEY OVERGROW THE

ROSTRAL ½ OF THE 4th VENTRICLE AND OVERLAP THE PONS AND MEDULLA

• THE FUSED PLATE SHOWS VERMIS IN THE MID LINE ANDTWO HEMISPHERES LATERALLY


• AT ABOUT THE END OF 4th MONTH FISSURES DEVELOP ON THE SURFACE AND THE FOLIA OF ADULT CEREBELLUM GRADUALLY DEVELOP

• A TRANSVERSE FISSURE SEPARATES THE NODULE FROM THE VERMIS AND THE FLOCCULUS FROM THE HEMISPHERES

• FLOCCULONODULAR LOBE IS THE MOST PRIMITIVE PART—THE ARCHICEREBELLUM –

• CONNECTED TO VESTIBULAR APPARATUS


• VERMIS AND ANTERIOR LOBE FORM THE • PALEOCEREBELLUM ASSOCIATED WITH

SENSORY DATA FROM THE LIMBS

• POSTERIOR LOBE FORMS THE NEOCEREBELLUM CONCERNED WITH SELECTIVE CONTROL OF LIMB MOVEMENTS


• HISTOGENESIS• NEUROBLASTS DERIVED FROM THE CELLS IN

THE VENTRICULAR ZONE MIGRATE TO THE SURFACE OF THE CEREBELLUM TO FORM THE EXTERNAL GRANULAR LAYER

• THESE CELLS RETAIN THE ABILITY TO DIVIDE AND FORM A PROLIFERATIVE ZONE ON THE SURFACE OF THE CEREBELLUM


• HISTOGENESIS [ CONTD ]• OTHER NEUROBLASTS REMAIN CLOSE TO THE

VENTRICULAR SURFACE AND DIFFERENTIATE INTO---

• 1 DENTATE NUCLEUS• 2 EMBOLIFORM NUCLEUS• 3 GLOBOSE NUCLEUS• 4 FASTIGIAL NUCLEUS

DEVELOMENT OF CEREBELLUM

• HISTOGENESIS [CONTD ]• IN THE 6th MONTH THE EXTERNAL GRANULAR

LAYER GIVES RISE TO VARIOUS CELL TYPES

• LAYERS OF CORTEX• 1 OUTER MOLECULAR LAYER• 2 MIDDLE PURKINJE LAYER• 3 INNER GRANULAR LAYER

DEVELOPMENT OF CEREBELLUM• HISTOGENESIS [ CONTD ]• MOLECULAR LAYER• TWO TYPES OF CELLS• 1 STELLATE • 2 BASKET CELLS• PURKINJE CELL LAYER• LARGEST NEURONS OF CNS [ GOLGI TYPE I ]• GRANULAR LAYER• TWO TYPES OF CELLS• 1 GRANULE CELLS—MOST NUMEROUS,SMALLEST AND ONLY

EXCITATORY NEURONS• 2 GOLGI TYPE 2/INNER STELLATE


• CEREBELLAR CORTEX REACHES ITS DEFINITVE SIZE AFTER BIRTH

• DEEP NUCLEI REACH THEIR FINAL POSITION BEFORE BIRTH

DEVELOPMENT OF CHOROID PLEXUS OF 4th VENTRICLE

• THIN EPENDYMAL ROOF IS COVERED EXTERNALLY BY PIA MATER

• TELA CHOROIDEA FORMED BY THESE TWO LAYERS

• TELA CH CONTAINS TUFTS OF BLOOD VESSELS• TELA CHOROIDEA INVAGINATES THE

VENTRICLE AND DIFFERENTIATES INTO CHOROID PLEXUS

DEVELOPMENT OF CHOROID PLEXUS

• CHOROID PLEXUS SECRETES CSF

• THIN ROOF EVAGINATES IN THREE LOCATIONS• THESE OUTPOUCHINGS RUPTURE TO FORM

THREE FORAMINA• 1 FORAMEN OF MAGENDIE--- MEDIAN • 2 FORAMINA OF LUSHKA---LATERAL

FUNCTIONAL COMPONENTS OF SPINAL & CRANIAL NERVES

• CELL COLUMNS OF OF BASAL PLATE• THREE ELONGATED BUT INTERRUPTED COLUMNS

FROM MEDIAL TO LATERAL• 1 GENERAL SOMATIC EFFERENT• CONTINUOUS WITH THE ANTERIOR GRAY COLUMN OF

SP CORD• IN THE CAUDAL PART OF HINDBRAIN REPRESENTED BY

HYPOGLOSSAL NUCLEI • REAPPEARS AT HIGHER LEVELS AS THE NUCLEI OF

CN6,CN4 &CN3

FUNCTIONAL COMPONENTS OF SPINAL &AND CRANIAL NERVES

• CELLS OF BASAL PLATE [ CONTD ]• 2 SPECIAL VISCERAL EFFERENT• REPRESENTED IN UPPER PART OF SP CORD AND

LOWER BRAIN STEM [MEDULLA & PONS ]• FOR THE SUPPLY OF PHARYNGEAL AND POST

PHARYNGEAL MUSCLES• CAUDAL BRAIN STEM PART GIVES FIBRES TO

CN9,CN10,CN11 AND FORM THE ELONGATED NUCLEUS AMBIGUUS [SUPPLIES LARYNX ,SOFT PALATE ,PHARYNX AND UPPER OESOPHAGUS ]

FUNCTIONAL COMPONENTS OF SPINAL AND CRANIAL NERVES

• CELLS OF BASAL PLATE [CONTD ]• SPECIAL VISCERAL EFFERENT CONTD• NUCLEUS AMBIGUUS CONTINUES INTO THE

CERVICAL PART OF THE SP CORD AS THE ORIGIN OF SPINAL ACCESSORY NERVE

• AT HIGHER LEVELS GIVES ORIGIN TO MOTOR NUCLEI OF CN7 & CN5


• 3 GENERAL VISCERAL EFFERENT• ALSO INTERRUPTED• REPRESENTED IN THE SP CORD BY THE LATERAL

GRAY COLUMN• CAUDAL PART FORMS SOME OF THE DORSAL

NUCLEUS OF VAGUS---MOTOR NEURONS SUPPLYING INVOLUNTARY MUSCLES

• CRANIAL PART FORMS THE SALIVATORY NUCLEUS

FUNCTIONAL COMPONENTS OF SPINAL CRANIAL NERVES

• CELL COLUMNS OF ALAR PLATE• FOUR INTRRUPTED COLUMNS FROM MEDIAL

TO LATERAL• 1 GENERAL VISCERAL AFFERENT• REPRESENTED BY A PART OF DORSAL NUCLEUS

OF VAGUS RECEIVING IMPULSES FROM THE VISCERA


• CELL COLUMNS OF ALAR PLATE [CONTD ]• 2 SPECIAL VISCERAL AFFERENT • REPRESENTED BY THE NUCLEUS OF TRACTUS

SOLITARIUS RECEIVING TASTE FIBRES• 3 GENERAL SOMATIC AFFERENT• REPRESENTED BY THE AFFERENT NUCLEI OF

CN5 RECEIVING IMPULSES FROM THE SURFACE OF THE HEAD

FUNCTIONAL COMPONENTS SPUNAL AND CRANIAL NERVRS

• CELL COLUMNS OF ALAR PLATE [ CONTD ]• 4 SPECIAL SOMATIC AFFERENT• REPRESENTED BY THE NUCLEI OF

VESTIBULOCOCHLEAR NERVE RECEIVING IMPULSES FROM THE EAR

DEVELOPMENT OF MIDBRAIN

• DEVELOPS FROM MESENCEPHALON• NEURAL CANAL NARROWS AND BECOMES THE

CEREBRAL AQUEDUCT WHICH CONNECTS THE 3rd & 4th VENTRICLES

• SULCUS LIMITANS SEPARATES THE ALAR PLATE FROM THE BASAL PLATE


• BASAL PLATE• CONTAINS TWO GROUPS OF MOTOR NUCLEI • 1 SOMATIC EFFERENT• REPRESENTED BY CN3 & CN4 WHICH

INNERVATE THE MUSCLES OF EYE • 2 GENERAL VISCERAL EFFERENT• REPRESENTED BY THE NUCLEUS OF EDINGER

WESTPHAL WHICH INNERVATES THE SPHINCTER PUPILLAE MUSCLE


• BASAL PLATE [CONTD ]• MARGINAL LAYER OF EACH BASAL PLATE ENLARGES

AND FORMS THE CRUS CEREBRI• CRURA SERVE AS PATHWAYS FOR

CORTICOPONTINE,CORTICOBULBAR AND CORTICOSPINAL FIBRES

• NEUROBLASTS POSSIBLY DIFFERENTIATE INTO NEURONS FORMING THE NUCLEI OF RED NUCLEUS,SUBSTANTIA NIGRA AND RETICULAR FORMATION


• ALAR PLATE• TWO ALAR PLATES AND THE ORIGINAL ROOF

PLATE FOPRM THE TECTUM• NEUROBLASTS DIFFERENTIATE INTO SENSORY

NEURONS OF SUP AND INF COLLICULI• COLLICULI APPEAR ON THE POSTERIOR

SURFACE OF THE BRAIN


• ALAR PLATE [CONTD ]• SUP COLLICULI---ASSOCIATED WITH VISUAL

REFLEXES• INF CILLICULI---ASSOCIATED WITH AUDITORY

REFLEXES• CELLS OF ALAR PLATE MIGRATING VENTRALLY

MAY GIVE RISE TO SUBSTANTIA NIGRA WHICH IS A BROAD LAYER OF GRAY MATER ADJACENT TO CEREBRAL PEDUNCLES

THANK YOU

development of brain

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