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 ~