Nervous system Embryology and Congenital Malformations Flashcards
Which layer of the trilaminar disc forms the neural tube?
Ectoderm
In which week of development does the CNS start to develop?
Week 3
What is formed when there is thickening of the ectoderm anterior to the primitive node?
Neural plate
What is formed when the edges of the neural edges move upward?
Neural folds
What is formed when the neural folds grow so much and start to move towards each other and eventually fuse?
Neural tube
Fusion of the anterior and posterior ends of the neural tube is delayed. What does this form?
Anterior and posterior neuropore
When does the anterior neuropore close?
Approx. day 25
When does the posterior neuropore close?
Approx. day 27
Failure of the neural tube closing properly results in neural tube defects.
Name three of the most common neural tube defects?
Anencephaly
Encephalocele
Spina Bifida
Who is more likely to develop anencephaly- males or females?
Females 4x more likely
What happens in anencphaly?
Anterior neuropore fails to close meaning the skull fails for form.
The lack of skull in Anencephaly means tissue is in direct contact with amniotic fluid. What does this cause to happen?
Brain tissue degenerates
Is anencephaly compatible with life?
No
What happens in Encephalocoele?
Herniation of cerebral tissue through a defect in the skull
What causes encephalocoele?
Failure of closure of the rostral neural tube.
Which region is encephalocoele most common in?
Occipital region
How does encephalocoele affect the child?
Variable degree of neurological deficits, depending on which area of the brain is affected.
What causes spina bifida?
Defective closure of caudal neural tube
Which tissues are affected by spina bifida?
Tissues overlying the spinal cord
In all forms of spina bifida, there is a defect in what?
Vertebral arches
What is the most common form of spina bifida?
Spina bifida occulta
Which type of spina bifida is the mildest?
Spina bifida occulta
What causes spina bifida occulta?
Failure of embryotic halves of vertebral arch to grow and fuse
Which vertebrae are affected by spina bifida occulta?
L5/6
->extra lumbar vertebrae due to bones not fusing:) 10% of population have it
A lot of the time, people with spina bifida occulta will not realise they have it.
Occasionally, what can mark the site of non-fusion?
Small patch of hair
What is spina bifida cystica?
Protrusion of the spinal cord and/or meninges through a defect in the vertebral arches
Which type of spina bifida cystica is the rarest and mildest?
Spina bifida with meningocele
What happens in spina bifida with meningocele?
Protrusion of meninges and CBF
What happens in spina bifida with meningomyelocele?
Herniation of neural tissue or nerves in the fluid filled sac.
What can spina bifida with meningomyelocle cause?
Neurological deficiencies- loss of sensation, muscle paralysis- depends on affected area
What is spina bifida with meningomyelocle associated with?
Hydrocephalous (build up of fluid in the brain).
Which type of spina bifida is the most severe?
Myeloschisis.
What happens in myeloschisis?
Failure of neural tube closure-spinal cord appears to be flattened and has no overlying membrane meaning tissue is exposed to amniotic fluid.
What should pregnant women take to reduce risks of neural tube defects in their child?
Folic acid supplements
All pregnant women are offered maternal blood screening to check for AFP. What does a high level of AFP mean?
AFP produced in foetal liver. If there is a defect, it can leak into amniotic fluid and then into maternal blood.
At which point in pregnancy is AFP best detected?
16-20 wks
What can be used to determine if high AFP is coming from the foetus rather than the mother?
Amniocentesis
What are some of the risk factors for neural tube defects?
Genetic predisposition
Nutrition
Environmental
Just for you, describe which aspects in the diet can lead to increased risks of neural tube defects.
Low folate
High vitamin A
Which drug can increase risks of neural tube defects?
Sodium valproate
During week 4 of development, there is development of the three primary brain vesicles. Which name is given to the forebrain vesicle?
Prosencephalon
During week 4 of development, there is development of the three primary brain vesicles. Which name is given to the midbrain vesicle?
Mesencephalon
During week 4 of development, there is development of the three primary brain vesicles. Which name is given to the hindbrain vesicle?
Rhombencephalon
The primary vesicles then split to form secondary vesicles. What does the prosencephalon divide to form?
Telencephalon
Diencephalon
The primary vesicles then split to form secondary vesicles. What does the rhombencephalon divide to form?
Metencephalon
Myelencephalon
What happens to the mesencephalon during the division of primary vesicles into secondary vesicles?
Remains as mesocephalon
Between which parts of the brain does the cephalic flexure develop?
Between midbrain and hindbrain
(mesencephalon and rhombencephalon)
Between which parts of the brain does the cervical flexure develop?
Hindbrain and spinal cord
Where does the pontine flexure develop?
In the brain
What does the telencephalon give rise to?
Cerebral hemispheres
Hippocampus
Basal ganglia
What does the diencephalon give rise to?
Thalamus
Hypothalamus
Pituitary gland
Pineal
What does the mesencephalon give rise to?
Superior and inferior colliculi
What does the metencephalon (division of hindbrain) give rise to?
Cerebellum
Pons
What does the myelencephalon (division of the hindbrain) give rise to?
Medulla
Why does the brain have folds?
To save space
Name the rare conditions where the brain is smooth and has no folds.
Lissencephaly
What causes lissencephaly?
Defective neuronal migration
Which condition occurs when there is an excessive number of small gyri?
Polymicrogyria
(think, poly=many, micro=small, gyria!)
The lumen of the neural tube forms the ventricular system of the brain.
Which ventricle is formed from the telecephalon?
Lateral ventricles
The lumen of the neural tube forms the ventricular system of the brain.
Which ventricle is formed from the diencephalon?
3rd ventricle
The lumen of the neural tube forms the ventricular system of the brain.
Which ventricle is formed from the mesencephalon?
Cerebral aqueduct
The lumen of the neural tube forms the ventricular system of the brain.
Which ventricle is formed from the metencephalon?
4th ventricle
The lumen of the neural tube forms the ventricular system of the brain.
Which ventricle is formed from the myelecephalon?
Central canal
In which week of development is CBF produced?
Week 5
Where is CBF produced?
Choroid plexus in the 3rd and 4th ventricles
What is hydrocephalous caused by?
Accumulation of CSF resulting in an enlarged brain and cranium
What is frequently the cause of hydrocephalus?
Blocked cerebral aqueduct
Which type of spina bifida is hydrocephalus associated with?
Spina bifida cystica
What type of epithelium does the neural tube have?
Pseudostratified epithelium
Neural tube produces most of the cells of the CNS.
Which cells don’t they produce?
Mesenchymal cells which are phagocytic cells
What does the PNS develop from?
Neural crest cells
Which type of nerve are spinal nerves?
Mixed- motor and sensory
Now for some very rare congenital anomalies-
Microcephaly (small brain).
What causes microcephaly?
Genetics
Drugs
Zika virus infection
Aegenesis of corpus callosum?
Corpus of callosum, which connects the two cerebral hemispheres is missing.
Porencephaly?
Formation of CSF filled cysts or cavities within the brain
What can cause porencephaly?
Postnasal stroke or infection
Schizencephaly?
Large clefts or slits in the brain
Why does schizencephaly occur?
Usually due to genetics or utero stroke or infection
What happens in split cord malformation (diastematomyelia)?
Spinal cord splits longitudally into 2
What can diastematomyelia cause?
Scoliosis
Intellectual impairment is a much more common problem to do with the functioning of our CNS.
Give an example of intellectual impairment with is genetic.
Down’s syndrome
What are some causes of intellectual impairment?
Genetic (Down’s)
Radiation
Infectious agents
Birth trauma
What is the most common cause of intellectual impairment?
Maternal alcohol abuse
When in development is the neural tube closed by?
End of week four
