DEVELOPMENT OF PROSENCEPHALON

PROSENCEPHALON(FOREBRAIN)

Telencephalon: Rostral part of forebrain

• Cerebral Hemispheres Diencephalon: Caudal &

median part • optic cup & stalk • Hypophysis/Pituitary• Thalmus• Hypothalmus• Epiphysis

DIENCEPHALON

• Roof plate• Alar plates = 2• Absent floor & basal plates

ROOF PLATE & EPIPHYSIS• Roof plate

1. Choroid plexus of 3rd ventricle

2. Most caudal part of roof plate develops into epiphysis/ pineal body

Pineal body• Appears as epithelial thickening in the

midline, but by 7th week it begins to evaginate

• Eventually it becomes a solid organ on the roof of mesencephalon

• Function: Respond to light and darkness & affect the endocrine and behavioral rhythms

• In adults calcium is frequently deposited in the epiphysis and then serve as land marks on radiographs of skull.

ALAR PLATES

• Forms lateral wall of diencephalon• A groove hypothalamic sulcus divides it

into:

1.Thalamus

2.Hypothalamus

THALAMUS

• Thalamus gradually projects into the lumen of diencephalon due to proliferation of cells

• Frequently the expansion is so great that two thalami fuse in mid line forming massa Intermedia or Interthalamic connexus

HYPOTHALMUS

• Forms the lower portions of alar plate

• Differentiate into number of nuclear masses that regulate visceral functions

• Mammillary body forms a distinct protuberance on the ventral surface of hypothalamus on each side of midline

Hypophysis/Pituitary Gland-Ectodermal

Develops from two sources:

1. An ectodermal outpocketing of the stomodeum---- Rathke’s pouch

2. Downward extension of diencephalon---- the infundibulum

Cont…

• At 3 weeks Rathke’s pouch appear as evagination that grows dorsally towards infundibulum.

• By the end of 2nd month it loses its connection with the oral cavity

• Comes to lie in close contact with infundibulum

Cont…• Cells in the anterior wall rapidly proliferate

and form the ---- anterior lobe/ adenohypophsis.

• A small extension of the lobe is pars tuberalis that surrounds the infundibulum

• The posterior wall of pouch forms the --- pars Intermedia

• Infundibulum give rise to stalk & pars nervosa----posterior lobe/Neurohypophysis

Hypophysis/Pituitary Gland-Ectodermal

HYPOPHYSEAL DEFECTSCRANIOPHARYNGIOMAS

Remnant of Rathke’s pouch

Cerebral Hemispheres• Arise by 5th week as bilateral evaginations of

lateral wall of forebrain • Interventricular foramen

CEREBRAL HEMISPHERES• Middle of 2nd month the basal

part/floor of hemispheres begins to grow & bulges into lumen of lateral ventricle & into floor of foramen of Monro

• In T.S this rapidly growing region has striated appearance therefore called Corpus striatum

• C.H become C-shaped• Choroid plexus develop in the

region where wall of hemisphere is attached to roof of diencephalon

CORPUS STRIATUM• As the cerebral cortex differentiates the axons passing to &

from the cortex (Internal capsule) break the nuclear masses into:

dorsomedial portion caudate nucleus ventrolateral portion the lentiform nucleus

• Medial wall of C.H fuse with lateral wall of diencephalon

CHOROID FISSURE

• The Lateral ventricle become C-shaped due to growth & curvature of C.H

• The caudal end of each C.H turns ventrally & then rostrally, forming the temporal lobe & in so doing it carries the ventricle (forming temporal horn) & Choroid fissure with it.

CHOROID PLEXUS

• Choroid plexus protrude in the lateral ventricle along the choroid fissure

• The thin medial wall of the C.H is invaginated along the choroid fissure by vascular pia matter to form choroid plexus of temporal horn

Growth of cerebral hemispheres• C.H grow in anterior, posterior

& inferior directions resulting in formation of frontal, occipital & temporal lobes.

• As growth in the region of corpus striatum slows the region b/w frontal & temporal lobes depressed & is called insula

• This region is later overgrown by other lobes Which completely covers it at birth.

COMMISSURES

• Anterior commissure- 1st to appear• Hippocamphal commissure• Corpus callosum- 10th week• Habenular commissure• Posterior commissure• Optic chiasma

Congenital anomalies

Cranium Bifidum

Holoprosecrphaly

Schizencephaly

Anencephaly

Hydrocephalus

Arnold Chiari Malformation