Embryo Flashcards
what is the function of the hippocampal commissure
connects the hippocampal formations
what is lissencephaly and what causes it
- sx
“smooth brain”
incomplete neuronal migration to cerebral cortex during 3-4 months gestation
- sx: seizures, mental deficiency, mild spastic quadriplegia
when do the forebrain and hindbrain divide
(forebrain into telencephalon and diencephalon, and hindbrain into metencephalon and myelencephalon)
5th week
what does the basal plate become
motor neurons that leave the CNS and travel to skeletal muscle
- ventral and lateral grey columns/horns
function of corpus callosum and how it develops
connects hemispheres along their length
- anterior portion forms first, posterior forms in fetal life
causes of hydrocephalus
- increased CSF production by choroid plexus adenoma
- intraventricular hemorrhage causing obstruction of lateral or median aperature
- congenital aqueductal stenosis
when do the basal ganglion and cortical structure develop
between weeks 6-32
how do the median and lateral apertures form and what is their purpose
the roof of the 4th ventricle evaginates in 3 locations and ruptures
–> allows CSF to enter subarachnoid space from the 4th ventricle
what type of neurons are found closest to the midline
GSE
the cavity of the metencephalon becomes what
superior part of 4th ventricle
list the 6 structures contained within the telencephalon
cerebral cortex
subcortical white matter
olfactory bulb and tract
basal ganglia
amygdala
hippocampus
clinical features of holoprosencephaly
microcephaly
microphthalmia
ocular hypotnesion
cleft lip w/ or w/o cleft palate
intellectual disabilites
epilepsy
hydrocephalus
where is the hypothalamus from
neuroblasts in the intermediate zone of the diencephalon
what does the embyronic cervical flexure do
demarcates hindbrain from spinal cord
what are the tegmental nuclei (red nuclei, reticular nuclei, CN III, and IV nuclei) formed from
neuroblasts from the basal plate
what does the mesencephalon give rise to
the midbrain
how do the alar and basal plates migrate
alar plates migrate to become lateral to the basal plates so motor nuclei develop medial to sensory nuclei
(affarent will be lateral to efferent)
what type of neurons are found closest to the sulcus limitans
GVA and SVA
what does the caudal eminence become
sacral and coccyx regions of spinal cord
besides the posterior pituitary, what else in the pituitary gland comes from neurohypophyseal diverticulum
median eminence
infundibular stem
what does the medulla oblongata consist of
olive
pyramid
where does the posterior pituitary come from
neurohypophyseal diverticulum from diencephalon
what does the epithalamus develop from
roof and dorsal portion of lateral wall of diencephalon
primordia of the retinae and optic nerves are from what
telencephalon
how does the white matter of the cerebral cortex form
axons from neurons in the cortical plate and subplate join those in the intermediate zone, which forms the white matter
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what is the septum pellucidum and how does it form
a thin plate of brain tissue containing nerve cells and fibers
- runs as a sheet from the corpus callosum down to the fornix separating the anterior horns of the left and right lateral ventricles of the brain
- forms from stretching of the lamina terminalis
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what part of the neural tube becomes the brain
cranial to the fourth somites
what does the rhombencephalon give rise to
(hindbrain)
metencephalon (pons)
myelencephalon (medulla)
when do the rostral and caudal neuropores close
rostral: day 25
caudal: day 27/28
how are the inferior and superior colliculi formed
neuroblasts of alar plate migrate into the tectum
what is the in the ventricular zone of the spinal cord
stem cells
ependymoblasts
choroid plexus cells
what does the prosencephalon give rise to
(forebrain)
telencephalone
diencephalon
what do the epithalamic sulcus and hypothalamic sulcus do
epithalamic: separates thalamus and epithalamus
hypothalamic: separates thalamus and hypothalamus
how and where does the cortical plate layer of the developing cerebral cortex form
a set of neurons migrates into the preplate layer and splits it, producing the cortical plate layer which lies in between the marginal zone and the subplate
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when does neurulation begin
day 22-23
what is in the intermediate zone of the spinal cord
grey matter
- neuroblasts
- astrocytes
primary neurulation gives rise to _____
lumbar region of spinal cord
what is rathke’s pouch from
first arch surface ectoderm
what is type I chiari malformation
inferior part of cerebellum herniates through foramen magnum
- most comon form
what are the radial glial cells in the developing cortex and what is their function
cells that extend the entire length of the cortex
- neurons migrate on the processes of these cells to migrate into the periphery
what are the cerebral hemispheres from
telencephalon
failure of site 2 in the neural tube to close causes what
meroencephaly (anencephaly)
describe how the preplate layer and then the intermeidate zone of the developing cerebral cortex forms
the first neurons from the ventircular zone form the preplate, and then axons extend on the inner side of the preplate to form the intermediate zone
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what factor controls proliferation and patterning of neuroepithelial cells with the GLI transcription factor
SHH
how are the nuclei gracilus and cuneatus formed
caudal myelencephalon neuroblasts in alar plates migrate into the marginal zone
what are pituicytes from
neuroepithelial cells
what is the function of the anterior cerebral commissure
connects olfactory bulb with the cerebral hemispheres
what is in the marginal zone of the spinal cord
oligodendrocytes
- axons that will eventually be myelinated
what are the cerebral peduncles (crus cerebri) formed from
fibers growing from the cerebral cortex
how does the choroid plexus from
ependymal roof of 4th ventricle –> forms tela choroida –> tela choroida invaginates into the 4th ventricle and differentiates into the choroid plexus
- happens similarly in 3rd ventricle
sx of agenesis of corpus callosum
(may be asymptomatic)
- seizures
- mental deficiency
what is the anterior pituitary from
hypophyseal diverticulum from the roof of the oral cavity
(Rathke’s Pouch)
defective closure of the rostral neuropore during the 4th week can cause what
anencephaly
meningoencephalocele (picture)
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how does craniorachischisis happen
failure of sites 1, 2, and 4 of the neural tube to close
what part of the neural tube becomes the spinal cord
caudal to the fourth somites
how are layers 5 and 6 formed in the developing cerebral cortex
the earliest neurons form here
how does the pineal gland form
develops as a median diverticulum of the caudal part of the roof of the diencephalon
failure of site 1 in the neural tube to close causes what
spina bifida cystica
compare spina bifida occulta, SB with meningocele, SB with meningomyelocele, and SB with myeloschisis
SB occulta: unfused neural arch, skin ramins intact, tuft of hair
SB w/ meningocele: meninges extrude
SB w/ meningomyelocele: meninges and neural tissue extrude
SB w/ myeloschisis: open neural tissue
where are the pons and cerebellum originated from
metencephalon
what does the third ventricle form from
cavities of telencephalon and diencephalon (but mostly diencephalon)
what is the sulcus limitans
separates alar and basal plates
what causes holoprosencephaly
incomplete separation of cerebral hemispheres
- genetic/environmental factors
- maternal diabetes
- teratogens (alcohol)
how are layers 2, 3, and 4 formed in the developing cerebral cortex
later neurons migrate through layers 5 and 6 and establish layers 2, 3, and 4
what is pachygyria
a type of lissencephaly where there are broad, thick gyri
what is the embyronic cephalic flexure
a bend between midbrain and forebrain
how is the cerebral aqueduct formed
the neural canal narrows between the 3rd and 4th ventricles
what part of the metencephalon forms the cerebellum
cerebellar swellings from the dorsal parts of alar plates
what does the alar plate become
dorsal horn
- sensory neurons that stay in the CNS
how is the interthalamic adhesion formed
the thalamus develops on each side of the 3rd ventricle and bulges in and fuses at midline, forming the adhesion
what cerebral commisures form first
anterior and hippocampal commissures
when does secondary neurulation occur
days 20-42
how does the falx cerebri form
mesenchyme gets trapped in the longitudinal fissure of the cerebral hemispheres
what is type II chiari malformation
cerebral tissue and brainstem herniate through foramen magnum
- often with occipital encephalocele and lumbar myelomeningocele
what is the roof of the mouth from
first arch ectoderm
what is neuronal heterotopia
cells are in aberrant positions compared to a normal brain
- commonly involve enlarged ventricles and malformation of corpus callosum
what does the embyronic pontine flexure do
divides hindbrain into caudal myelencephalon and rostral metencephalon
causes of microcephaly
- autosomal recessive
- ionizing radiation
- infectious agents
- maternal alcohol abuse
list the 4 structures in the diencephalon
thalamus
hypothalamus
epithalamus
optic nerve (eye)