The document outlines the development of the central nervous system (CNS), detailing the process of neurulation, spinal cord formation, and the progression of brain structures including primary and secondary brain vesicles. It describes the formation of the eye and ear, highlighting key anatomical changes such as the development of optic structures and the division of the ear into external and middle components. Comprehensive stages of growth and structural organization within the CNS are emphasized throughout the document.

1. Development of CNS

2. Neurulation
• Ectoderm overlying the notochord
thickens-neural plate
• Development of mesoderm on either
side of notochord
• Neural fold formation
• Neural groove
• Movement of neural folds towards
each other –neural tube
• Anterior (25th day)and posterior
neuropore(27th day)
• Cranial part and caudal part

4. Neural crest cells
• Cells at the tips of neural folds
break away from the
neuroectoderm –neural crest
cells.
• Do not participate in neural tube
formation
• Neural crest cells between
neural tube and surface
ectoderm

5. Formation of ectodermal placodes
• Neural fold –neural crest cells and neuroepithelial cells
• Neuroepithelial cells get incorporated into the surface
ectoderm.- ecodermal placodes

6. Spinal cord development
• Neural tube increases in
thickness
• 5th week of IUL-T.S,of neural
tube-matrix zone,mantle
zone,marginal zone
• Matrix zone-neuroblasts and
spongioblast-neurons and
neuroglial cells
• Mantle zone-spinal gray
matter
• Marginal zone-white matter

7. Development of Functional columns
• Neural tube cavity-vertical slit
• Dorsal and ventral walls of NT-roof
and floor plates.
• Thickening of lateral wall-sulcus
limitans –dorsal and ventral walls
• Dorsal lamina/alar lamina-
sensory/afferent
• Ventral lamina/basal lamina-
efferent/motor
• Spinal nerve

8. Functional components
• Alar lamina
• General somatic afferent: superficial
and deep receptors
• General visceral afferent:
thoracolumbar and sacral regions-
viscera and blood vessels
• Basal lamina:
• General visceral efferent:
thoracolumbar and sacral regions-
viscera and blood vessels
• General somatic efferent:innervate
skeletal muscles

9. Positional changes of spinal cord
• 8 weeks-equal length
• 24 weeks-S1 vertebra
• Birth-L3 level
• Adults-L1 level

10. Brain development
• Primary brain vesicle:
Prosencephalon
• Mesencephalon
• Rhombencephalon
• Secondary brain vesicle:
• Prosencephalon-telencephalon and
diencephalon
• Rhombencephalon:metencephalon
• (pons and cerebellum)and
myelencephalon(medulla)

12. Flexures of the brain
• Pontine flexure:middle
of rhombencephalon
• Cephalic:regions of
midbrain
• Cervical
flexure:rhombencephalon and
spinal cord.
• Cephalic and Cervical flexure
concave ventrally

13. Pontine flexure
• Hindbrain is folded-acute angle
ventrally
• Cavity becomes diamond shaped-IV
ventricle
• Wide at the middle-tapers superiorly-
aqueduct of Sylvius
• Inferiorly-central canal of medulla
• Thin roof is pulled out to cover the
space posteriorly
• Line of folding-lateral recess
• Flattening of hindbrain , due to
folding
displaces alar lamina lateral to basal
lamina

14. • Cervical flexure: convex dorsally
and present at the junction
between spinal cord and
hindbrain
• Cephalic flexure: convex dorsally
and appears at midbrain level.

15. Ventricular system
• Hindbrain-fourth ventricle
• Mesencephalic cavity:cerebral
aqueduct
• Diencephalic cavity:third ventricle
• Telencephalic cavity:lateral ventricle

16. Hindbrain
• Floor of IV ventricle-myelencephalon and metencephalon
Basal and alar lamina

17. Development of eye
• Diverticula from lateral wall of
diencephalon
• Optic vesicle and optic stalk
• Optic vesicle grows laterally and
comes close to the surface
ectoderm.
• Induces the surface ectoderm to
from the lens placode

18. • Lens placode detaches from the surface
and develops into lens vesicle
• Depression in optic vesicle to form optic
cup
• 2 layers-outer and inner
• Intra retinal space:space b/w 2 layers
• Pigment layer-outer layer of optic cup
• Posterior 4/5 of the inner layer-neural
retina
• Anterior 1/5 –choroid,ciliary body and
posterior surface of iris

20. • Optic cup receives the lens
vesicle
• Elongation of cells in the
posterior wall of lens vesicle
it
becomes a solid transparent
biconvex structure.
• Mesenchyme: suspensory
ligament of lens and
vitreous body
• Pupil :margin of optic cup

21. • Optic stalk develops a fissure-
choroid fissure
• Choroid fissure carries hyaloid
artery –posterior part of the
lens.
• Optic stalk:optic nerve.

22. Development of Ear
• External Ear – Pinna or the
auricle is formed by the Six
Cartilaginous masses present on
the either side of EAM.
• EAM- develops from First
Ectodermal cleft.

23. Middle ear
• First pharyngeal pouch and dorsal part of Second pharyngeal pouch – Tubo-tympanic recess.
• Medial part – Auditory tube
• First pharyngeal Arch Mesoderm – malleus, incus
• Second pharyngeal Arch Mesoderm - Stapes

24. Tympanic membrane
• External – Ectoderm of first Cleft
• Internal – Endoderm of Tubo-Tympanic Recess
• Middle Mesoderm between First Cleft and
Pouch