Embryology and abnormalities Flashcards
what induces the ectoderm to form neural plate and tube
notochord
what are the three germ layers
ectoderm, mesoderm, endoderm
primary neurulation, secondary neurulation
1-neural plate>folds and groove>tube. 2- forms spinal segments below S2.
types of spina bifida in increasing order of severity
oculta, lipoma and lipocele, cystica (meningocele, meningomyelocele), rachischisis
what defects do you see with meningomyelocele
sensory and motor in bowel, bladder, lower limb
tethered cord syndrome: problem with 1* or 2* neurulation? what happens? Results in?
Seconday. fibrous bands pull down on cord. Arnold-Chiari and hydrocephalus
Types of exencephaly
encephalocele (w/ or w/o brain tissue). Anencephaly (most common cause of stillbirths)
Name the primary brain vesicles
prosencephalon (forebrain), mesencephalon (midbrain), rhombencephalon (hindbrain)
name secondary brain vesicles and what comes from them
telencephalon (cereb hemis), diencephalon (thal,hypothal), mesencephalon (midbrain), metencephalon (pons, cerebellum), myelencephalon (medulla)
folding of the midbrain in the ventral direction. consequences
cephalic flexure. vertical orientation of cord and brianstem, horizontal orientation of forebrain
two defects in ventral induction
holoprosencephaly, agenesis of the corpus callosum
three layers of neural tube
neuroepithelial layer (all cells of cns except microglia), mantle layer (gray matter), marginal layer (white matter)
two parts of mantle layer and what divides them
basal (somotomotor [ant] and visceromotor [lateral]) and alar plates (sensory [post]). Sulcus limitans
what do the roof and floor plates of enural tube form?
commissures where axons cross from one side to the other
when does myelination occur
4th gestational month to end of second year
in ventricles: what happens to basal and alar plates? roof plate?
form medial motor and lateral sensory areas divided by sulcus limitans. Roof plate gets covered by pia to form tela choroidea which invaginates to form choroid plexus
four steps necessary to form cerebral hemispheres
proliferation, migration, organization, myelination
describe proliferation and migration and organization stages
neuroblasts and glioblasts. Neurblasts migrate along radial glia, pass cells of earlier birth, form 6 layers of cortex
defects in proliferation phase
microcephaly, macrocephaly, tuberous sclerosis, focal cortical dysplasia
defects in neuronal migration
seizures (abnormal conduction), lissencephaly, schizencephaly, focal dysgenesis, heterotopias
when does neurulation begin
day 17
what affects 2/3 of all NTDs
folate metabolism. All women of child bearing age should take it
Relationship of radial glial cells and neurons in cortex
same stem cells gives rise to glial then neurons. Radial cells move from ventricular zone to SVZ then back and forth escorting new cells
diastomyelia
notochord is split by adhesion b/w endo and ectoderm
what genes are mutated in classical lissencephaly. What do they affect
LIS1, DCX. Microtubule formation
subcortical band herterotopia: what? what mutation? what gradient?
bands of grey matter b/w cortex and lat. ventricles. DCX mutation (A>P gradient)
males with dcx get___. females get___. What inheritance? what protein does it produce
lissencephaly, subcortical band heterotopia. X-linked! Doublecortin
problems of organization phase
polymicrogyria. Predilection for perisylvian areas.
implication of malformation of cortical development (MCD)
epilepsy, learning disability, cerebral palsy, developmental delay
Three ways primary neurulation can go awry
diastomyelia, premature disjunction of neural tube from ectoderm (lipomas), nondisjunction (myelomeningocele)
