embryology and congenital malformations Flashcards
what does the nervous system develop from?
embryonic ectoderm
when does the CNS appear?
beginning of the 3rd week of pregnancy
what is the neural plate?
thickening of the ectoderm anterior to the primitive node
how are the neural folds formed?
the edges of the neural plate thicken and move upwards
how is the neural tube formed?
neural folds migrate towards each other and fuse at the midline
when does the anterior (cranial/rostral neuropore) part of the neural tube close?
around 25 days
when does the posterior (caudal neuropore) close?`
day 27
what defects can present as a result of the neural tube failing to close properly?
anencephaly
encephalocoele
spina bifida
what is anencephaly?
failure of the anterior neuropore to close
what is the result of the anterior neuropore failing to close?
skull fails to form
brain tissue degenerates
what is craniorachischisis?
failure of anterior neuropore and rostral neural tube to close
what is encephalocoele?
herniation of cerebral tissue through a defect in the skull
what causes encephalocoele?
failure in closure of the rostral neural tube
what causes spina bifida?
defective closure of the caudal neural tube
what is spina bifida?
non fusion of the vertebral arches
what is spina bifida occulta?
failure of the embryonic halves of the vertebral arch to grow normally and fuse
what is spina bifida cystica?
embryonic halves of the vertebral arch fail to grow normally and fuse AND the spinal cord and/or meninges can protrude through the defect
what are the 3 types of spina bifida cystica?
with meningocele
with meningomyelocle
with myeloschisis
what is spina bifida with meningocele?
protrusion of the meninges and CSF
what is spina bifida with meningomyelocle?
when the nerve roots and/or spinal cord are included in the protruding sac
what symptoms can present with SB with meningomyelocele?
neurological deficits - loss of sensation and muscle paralysis
what is SB with meningomyelocele associated with often?
hydrocephalus
what is myeloschisis?
when the spinal cord in the affected area is open due to the failure of the neural folds to fuse
what measures are taken to try and prevent neural tube defects?
folic acid supplements
how can neural tube defects be diagnosed prenatally?
maternal blood screening
amniocentisis
ultrasounf
what are some risk factors for NTD?
genetic predisposition
nutritional
environmental
when does development of the brain vesicles begin?
with closure of the anterior neuropore
what is the prosencephalon (forebrain) composed of?
telencephalon
diencephalon
what is the rhombencephalon (hindbrain) composed of?
metencephalon
myelencephalon
when does the cephalic flexure appear?
end of the 3rd week
where is the cephalic flexure located?
between the midbrain and the hindbrain
when does the cervical flexure appear?
end of the 4th week
where is the cervical flexure located?
between the hindbrain and the spinal cord
when does the pontine flexure appear?
5th week
where is the pontine flexure located?
in the hindbrain between the metencephalon and myelencephalon
what develops from the telencephalon?
cerebral hemispheres
hippocampus
basal ganglia
what develops from the diencephalon?
thalamus
hypothalamus
pituitary gland
pineal gland
what forms the ventricular system of the head?
lumen of the neural tube
when does CSF begin to form?
5th week of pregnancy
how does CSF drain into the subarachnoid space?
via openings in the roof of the 4th ventricle
where is CSF absorbed?
into the venous system
what is hydrocephalus?
accumulation of CSF
what does hydrocephalus result in?
enlarged brain and craniam
what is a common cause of hydrocephaly?
blocked cerebral aqueduct
what can cause i blocked cerebral aqueduct?
genetic
prenatal viral infection
IV haemorrhage
what kind of cells make up the neural tube
single layer of rapidly dividing neuroepithelial cells
what kind of epithelium makes up the neural tube?
pseudostratified epithelium
what cells of CNS are not produced by neuroepithelium?
microglia
what nevous system are neural crest cells part of?
PNS
what process of neural crest cells forms the body of the spinal cord?
peripheral process
what process of neural crest cells forms the dorsal horn of the spinal cord?
central process
how long is the spinal cord in the 3rd month of pregnancy?
entire length of vertebral column
what forms sympathetic and parasympathetic ganglia?
neural crest cells
how are sulci and gyri of the brain formed?
rapid growth of the cerebral hemispheres
what causes lissencephaly?
defective neuronal migration
what is lissencephaly?
failure of gyri and sulci to develop?
what does lissencephaly cause?
severe mental impairment
failure to thrive
seizures
abnormal muscle tone
what is polymicroglia?
excessive number of small gyri
what is porencephaly?
CSF filled cysts or cavities in the brain
what is schizencephaly?
large clefts or slits in the brain
what is diastematomyelia?
spinal cord split longitudinally into 2 parts
what are some symptoms of diastematomyelia?
scoliosis
weakness of lower extremities
loss of sensation
what is a common cause of newborn intellectual impairment?
maternal alcohol abuse
