Nervous system embryology and malformations Flashcards
Does the nervous system develop from ectoderm, mesoderm or endoderm?
ectoderm
What week does the CNS appear?
3
What is the neural plate?
Thickening of ectoderm anterior to the primitive node
What are neural folds?
Edges of the neural plate thicken and move upwards to form these
How is the neural tube formed?
Neural folds migrating towards eachother and fusing in the midline
Is the neural tube initially open or closed?
open
When does the anterior and posterior neuropore close?
anterior = day 25 posterior = day 27
What can failure of the neural tube closing lead to? Give 3 examples
death
NTD = spina bifida, anencephay, encephalocoele
Which neural tube defect is incompatible with life?
anencephaly
Is anencephaly more common in males or females?
females by 4 times
What happens in anencephaly?
anterior neuropore fails to close and the skull fails to form leading to brain tissue degeneration
Craniorachischisis
Entire neural tube fails to close
What is encephalocoele and what causes it?
Herniation of cerebral tissue through a defect in the skull due to failure of rostral tube closure
Where is encephalocoele most common?
occipital region
What causes spina bifida?
Defective closure of the caudal neural tube
What is affected in spina bifida?
tissue overlying spinal cord
What is spina bifida?
non-fusion of vertebral arches
Spina bifida occulta - what causes it?
failure of embryonic halves of vertebral arches to grow normally and fuse
What vertebral level does spina bifida occulta occur and what is a sign?
L5/6
dimple with patch of hair
What is spina bifida cystica?
Protrusion of spinal cord and/or meninges through vertebral arch defect
Spina bifida with meningocele - what is protruding??
CSF and meninges
spina bifida with meningiomyelocle - what else is included in the protrusion?
nerve roots/spinal cord - neurological defecit
What is spina bifida with meningiomyelocle associated with?
hydrocephalus
What is myeloschisis?
Rare form and most severe of spina bifida
spinal cord open in affected area as neural tube fails to close
4 prevention methods of spina bifida/NTD
folic acid supplements
ultrasound
amniocentesis
blood test
What are you looking for in the blood in prenatal diagnosis of NTDs and why?
AFP - alphafetoprotein
from foetus liver which means an open communication
Risk factors for NTDs
genetic predisposition
Nutrition - too much vitamin A, too little folate
Environmental eg sodium valproate, hyperthermia
Name the 3 primary brain vesicles
Prosencephalon
mesencephalon
rhombencephalon
Name the 5 secondary brain vesicles
Telencephalon diencephalon mesencephalon metencephalon myencephalon
When does the cephalic flexure form and where is it?
end of 3rd week
between midbrain and hindbrain
When does the cervical flexure form and where is it?
End of 4th week
between hindbrain and spinal cord
When does the pontine flexure form and where is it?
5th week
in hindbrain
Name the 3 flexures of the vesicles
cephalic
cervical
pontine
What does the telencephalon form?
cerebral hemispheres
hippocampus
basal ganglia
What does the diencephalon form?
thalamus
hypothalamus
pituitary gland
pineal
What does the mesencephalon form?
superior and inferior colliculi
midbrain
What does the metencephalon form?
cerebellum
pons
What does the myencephalon form?
medulla
What does the caudal neural tube form?
spinal cord
What does the lumen of the neural tube form?
ventricular system
When does CSF begin to form?
week 5
What is hydrocephalus and what is the main cause?
Accumulation of CSF resulting in enlarged brain and cranium
usually due to blocked aqueduct so lateral and 3rd ventricle cannot drain into 4th ventricle to be absorbed
Causes of hydrocephalus
genetics
prenatal viral infection
intraventricular haemorrhage
spina bifida cystica
The neural tube is initially a single layer of…..cells
neuroepithelial
What do the neuroepithelial cells go on to form?
Neurons, astrocytes, oligodendrocytes, ependymal cells - CNS
What is microglia formed by?
mesenchymal cells - mesodermal in origin
What do neural crest cells go on to form?
cells of PNS, autonomic NS and non neuronal cells eg melanocytes, adrenal medulla, meninges, facial bones and cartilage
How does the spinal cord position change?
initially entire length of vertebral column but then dura and vertebral column grow more rapidly
What is lissencephaly?
smooth brain - no sulci or gyri
What do people with lissencephaly normally die of?
problems with swallowing and aspiration
Polymicrogyria - what is it and what are the symptoms?
excessive number of small gyri
variable - mental retardation, seizures, motor defecits
What is microcephaly and give a recent common cause of this
small brain
Zika virus
What is porencephaly and what does it usually follow?
CSF filled cysts or cavities
postnatal stroke or infection
What is schizencephaly?
Large slits or clefts
What is diastematomyelia and what are the symptoms/signs?
split cord longitudinally
vertebral anomalies, scoliosis, hairy patch, loss of sensation
Causes of intellectual impairment
Formation of brain cells affected due to maternal alcohol, genetic, radiation, infection, birth trauma, postnatal insults eg meningitis
