Development
of the
Nervous System
Lesson 4
Development of the Brain
Adult brain structure product of…
 Genetic instructions
 Cell-to-cell signals
 Interaction b/n child and external
world
 Early development
 Before synaptogenesis
 Activity-independent
 Critical periods ~

Gastrulation & Neuralation
Gastrulation
 Invagination of embryo
 single sheet of cells  3 cell layers
 Formation of notocord
 Neuralation
 Induction signals from notocord…
 To neuroectoderm
 Growth of neural precursor cells~

Neural Induction
Induction signals
 From embryonic tissue
 Modulate gene expression
 Retinoic acid
 Steroid hormone
 Peptide hormones
 Fibroblast growth factor (FGF)
 Transforming growth factor (TGF)
 Sonic hedge hog (shh) ~

Retinoic Acid – Jekyl & Hyde?


Vitamin A derivative
 Too little 
abnormal
development
 Too much 
abnormal
development
Inductive signal
 Critical period
 Localization ~
Sonic Hedge Hog (SHH)




Induction of motor neurons
 Mutations  diseases
Holoprosencephaly (1/16 k births)
 Prevents bilateral development
 Division of hemispheres
 facial features (cyclopean eye)
Medulloblastoma
 Most common childhood tumor
Basal cell carcinomas of skin
 750 k/yr ~
Embryological Origin

Embryo has 3 layers
 endoderm
internal organs

mesoderm
muscles & skeleton

ectoderm
nervous system & skin ~
Embryological Origin
At 18 days
 Neural plate forms
 sheet of cells
 At 20 days
 Neural groove
 folds rostral to caudal will
form tube ~

Development of N.S.
At 22 days
 Neural tube
 CNS develops from walls

spina bifida - caudal tube
fails to close

as tube develops dorsal
portion pinches off &
forms...~
Development of N.S.
At 24 days
 Neural crest
 develops into all
neurons of PNS
 Mesoderm
 somites 
vertebrae & muscles ~

Differentiation
Specialization of
structures
 3 primary vesicles
 rostral end of tube
 develops into brain
 Prosencephalon  forebrain
 Mesencephalon  midbrain
 Rhombencephalon  hindbrain ~

Prosencephalon

Secondary vesicles
form & separate
 optic  retinas
retina & optic nerve CNS
not PNS


telencephalic  telencephalon
remainder  diencephalon ~
Other Primary Vesicles
Mesencephalic  mesencephalon
 dorsal - tectum
 ventral - tegmentum
 tube - cerebral aqueduct
 Rhombencephalic
 rostral - metencephalon
 caudal - myelencephalon
 tube - 4th ventricle ~

Neural Tube Defects: Rostral
Neural tube fails to close
 anencephaly
 skull & brain partially or totally absent
 perinatal mortality
 Encephalocele
 parts of brain protrude outside skull
 mental disability depends on extent ~

Neural Tube Defects: Caudal
Spina Bifida
 Cleft spine
 Spina bifida occulta
 40% of Americans
 Spina Bifida Manifesta
 1 in a 1000 births
 0.1% ~

Occulta
Spina Bifida Manifesta
Meningocele (*4%)
 SC/nerves not in sac
 less severe, repaired
 Myelomeningocele (*96%)
 SC/ nerves in protruding
 paralysis, incontinence,
learning disabilities
 hydrocephalus

can cause severe brain damage ~
Neural Tube Defects: Prevention
Possible genetic component
 reoccurrence in families
 ethnic/racial relationship
 Folic Acid (Folate) Deficiency
 50-70% of cases preventable
 CDC guidelines
not planning pregnancy: 400 mg/day
planned pregnancy: 4000 mg/day

under direction of health care provider ~