Neuroembryology SDL Flashcards
this forms the notochord
midline axial mesoderm
the notochord induces the overlying ectoderm to form the____
neural plate
ectoderm germ layer
neural tube & neural crest derivatives; CNS, PNS, sensory epithelium of nose, eye and ear, pituitary gland, mammary glands, epidermis, hair, nails, sweat glands, enamel of teeth, some eye mm
mesoderm germ layer
dura mater and connective tissue envestments of peripheral nerves
endoderm germ layer
parenchyma of the tonsils, thyroid, parathyroid, thymus
lumen of the notochordal canal transiently connects the amniotic cavity with the yolk sac to form the _____
neuroenteric canal
cells in the neural plate constitute the
neuroectoderm
separation of the neural tube from the surface ectoderm
dysjunction
these cells undergo an epithelial-mesenchymal transition and migrate away from the neuroectoderm to enter adjacent embryonic mesoderm
neural crest cell
neural crest cell derivatives
Schwann cells & glial cells of PNS; DRG; spinal & cranial nerve ganglia; leptomeninges (pia & arachnoid); ANS (simp & parasymp postgang); mesenchyme of pharyngeal arches (connective tissue/bones of the face and skull, dermis of face/neck, thyroid C cells, conotruncal septal heart cells); adrenal medulla cells; pigment cells (melanocytes)
completion of this marks the end of primary neurulation
ectoderm fusion (at ends of neural tube); anterior neuropore @ day 25 & posterior @ day 27
coalescence of caudal mass mesenchymal
cells into a rod followed by cavitation to form a tube & fusion with primary neural tube
secondary neurulation
levels involved in primary & secondary neurulation
C1-S2 & S3-Co (or C1-S1 & S2-Co)
folic acid in pregnancy: how much, when why?
400 ug/day; 2 months prior to conception; 70% reduction in NTDs
spina bifida occulta typically occurs in this region & is what type of neurulation defect
lower lumbar/upper sacral; secondary neurulation defect
failure of the secondarily formed neural tube to join the neural tube formed from primary neurulation & exs of this
secondary neurulation defect; spina bifida occulta, tethered spinal cord, caudal regression syndrome, diastematomyelia
an absence of lamina and spines that occurs in the upper regions of the vertebral column arise from what & cause what condition
arise from incomplete fusion of posterior neuropore during primary neurulation; cause spina bifida occulta
total failure of neurulation, no dysjunction; can occur in spinal cord or brain region; most severe NTD
rachischisis; craniorachischisis
failure to close anterior neuropore at cranial end of neural tube by day 25 during primary neurulation (C1-S2 level); most of brain doesn’t develop as a result
anencephaly
failure of posterior neuropore closure (neural plate caudal to neck is open)
myeloschisis
defect in vertebral arches covered by skin & usually doesn’t involve underlying neural tissue; failure to close posterior neuropore on day 27 at caudal end of neural tube during primary neurulation (C1-S2 level but most common at S1-S2); Failure of sclerotome cells to migrate into the region dorsal to the neural tube leading to the absence of vertebral arches in that region
spina bifida occulta
defect with protrusion of meninges or neural tissue
spina bifida cystica
a fluid-filled sac of meninges protrudes through the defect
meningocele
partial failure of posterior neuropore closure; neural tissue & meninges included in the fluid-filled sac protruding through the defect; most severe spina bifida NTD & occurs by day 27
myelomeningocele
anterior neuropore defect where brain & meninges protrude through opening in skull; partial failure occurs by day 25
encephalocele
persistence of neurenteric canal causes split spinal cord; a secondary neurulation prob
Diastematomyelia
caudal end of cord fixed by fibrous bands; lipomas (fat pads) often associated w this; a secondary neurulation prob
Tethered spinal cord
sacral hypoplasia/hypolastic femors (caudal dysgenesis); a secondary neurulation prob
Caudal regression syndrome
ventral induction defect; failure to form 2 cerebral hemispheres; fails to cleave & remains fused as single midline entity; alcohol & maternal diabetes may be risk factors; shh may be involved; occurs in wks 5-6
holoprosencephaly
cleft brain; disorder of migration in month 3-5
schizencephaly
smooth brain ( few gyri); disorder of migration in month 3-5
lissencephaly
broad gyri (too few gyri); disorder of migration in month 3-5
pachygyri
small gyri (too many gyri); disorder of migration in month 3-5
polygyri
Persistence of the neuroenteric canal leads to adhesions that can cause what developmental anomalies?
tethered spinal cord, malrotation of gut, neuroenteric fistula, dorsal dermal sinus tracts/cysts, split spinal tract
this is formed from the lumen of the notochordal canal to connect the amniotic cavity w the yolk sac
neural enteric canal
what secretes GFs in primary neurulation?
notochord
neural crest cells give rise to what of the PNS?
DRG & Schwann cells, meninges, sympathetic neuroblasts, mesenchyme of pharyngeal arches
NTD risk factors
- Folic acid deficiency (alcoholics, nutritional deficiency)
- Diabetic mothers
- Antiepileptic drugs
- Previous pregnancy with NTDs
- Hyperthermia (hot tubs)
which protein would increase in maternal serum and amniotic fluid in cases of a neural tube defect?
alphafetoprotein
what induces overlying ectoderm to differentiate into neuroectoderm?
Shh
what promotes dorsoventral differentiation of the spinal cord?
opposing Shh & BMP concentration gradients
what is formed by the alar plate under influence of BMPs?
dorsal (sensory) spinal cord
what is formed by the basal plate under the influence of Shh?
ventral (motor) spinal cord
which cells give rise to neuroblasts in the developing spinal cord?
neuroepithelial cells in wall of neural tube
which cells give rise to the astrocytes and oligodendroglia?
gliablasts (pseudostratified layer of neuroepithelial cells in wall of neural tube )
what is the function of the radial glia in the developing cerebral cortex?
function as scaffolds for neuronal migration & then become astrocytes
underlying cause of schizencephaly, lissencephaly, pachygyri or polygyri?
disruption of fetal neuronal migration due to various reasons
spatial and temporal differences in what genes are important for anterior-posterior axis development, neural tube segmenting, and secondary neurulation?
homeobox genes
imp for ventral induction
Shh
Why does maturation of spinal cord proceed in a rostral-caudal direction?
FGF secreted in gradient (low rostrally, high caudally) that maintains immaturity of caudal neural progenitor cells
This pseudostratified layer gives rise to neurons, astrocytes, oligodendrocytes, & then ependymal cells
neuroepithelial cells in wall of neural tube
What form the mantle layer surrounding the neural tube, “gray matter of the spinal cord”
neuroblasts
This layer surrounds the neural tube and contains nerve fibers from the neuroblasts in the mantle layer; forms the outmost layer of spinal cord
marginal layer
Thickening of this layer dorsally forms the alar plate & basal plate
mantle layer
the alar plate is
dorsal horn-sensory
the basal plate is
ventral horn-motor
These primitive nerve cells form a zone around the neuroepithelial layer called the mantle layer, which later forms the gray matter of the spinal cord
neuroblasts
imp for dorsal induction
BMP
derived from vascular mesenchyme (mesoderm) when blood vessel grow into nervous system
microglial cells
derived from neuroepithelial cells after neuroblasts forms
glial cells
- mantle layer-astrocytes
- marginal layer-oligodendrocytes
when neuroepithelial cells cease to produce neuroblasts & gliablasts they differentiate into this cell type which lines the central canal of spinal cord
ependymal cells
these form sensory ganglia (DRG), sympathetic
neuroblasts, Schwann cells, pigment cells,
odontoblasts, meninges, and mesenchyme of the pharyngeal arches
neural crest cells
herniation of part of cerebellum into foramen magnum is called what & can obstruct the flow of CSF & cause this condition
Arnold-Chiari; hydrocephaly
