Embryo Flashcards
what are 2 mechs. creating a neural tube
- primary neurulation - primary neurla tube from neuroectoderm and nerual plate
- secondary neurolation - secondary tube from mesoderm left from primitive stalk
what are 2 main steps to primary neurulation
- induction of neuroectoderm from neural plate
2. elevation apposition, contact and fusion of the folds
what organizes neuroectoderm
notochord
where does closure begin
in what will be cervical and goes rostral and caudal
what are ends where fusion occurs called
rostral and caudal neuropores
what happens at the caudal end of neural closure
medullary cord condense and tube extends into it and undergoes mesenchymal condensation
what does this caudal neurulation form?
the sacrum
what is freq. of neural tube defects
1:1000
what are risk factors for defects
Hx of defects, diabetes, obesisty, anticonvulsant meds — most women have none
what lowers risk
folic acid
what is unclosed rostral pore
anencephaly
what is arnold chiari malformation
posterior cransial fossa too small and foramen of mygandi compressed to get hydrocephalus
what are 2 ultrasound signs of spina bifida
lemon sign - flattening of frontal bone
banana sign - curved contour of cerebellum
what are 2 steps of shaping the neural tube
- dev. of brain vesicles
2. dev. of brain flexures
what are primary vesicles (3)
- proencephalon
- mesencephalon
- rhombencephalon
what are secondary vesicles and what will they become (5)
- telencephalon - hemispheres
- diencephalon
- mesencephalon - midbrain
- metencephalon - pons and cerebellum
- myencephalon - medulla
what are the 3 flexures
- midbrain flexure
- cervical flexure
- pontine flexure
what forms intermediate zone
migration of neurobalst and glioblasts toward outer wall (will be grey matter)
what forms marginal zone
extension of neuroblasts even further out (will form white matter)
what happens to cells that remain adjacent to neural tube
ependymal cells
what are layers of tube from in to out
ventricular>intermediate>marginal
how is grey matter established in cortex
radial glial cells extend out into margins and primitive neuroblasts migrate along them
what are dorsal and ventral thickening of intermediate zones
- dorsal - alar plates
2. ventral - basal plates
what do these plates become
- alar plates - interneurons
2. basal plates - motor neurons
what signalling proteins are used to differentiate floor from roof
floor releases SHH - basal plates
roof releases BMP -alar plates
what causes the outward flaring of alar plates at the medulla and pons
the pontine flexure
what are 2 consequences of the faster growth of the vert than the cord
- dissociation of the cord from vert. segments
2. cauda equina
what 2 things is PNS developed from
- neural tube
2. neural crest
what does the tube contribute to
- lower motor neurons
2. preganglionic autonomic neurons
what do the crest cells become
- dorsal root ganglia
2. post-ganglionic neurons of autonomic system
