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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 wallsspina 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 g/day
planned pregnancy: 4000 g/day under direction of health care provider ~