Session 1: Development of the Central Nervous System Flashcards
Explain how neural tube defects come about.
Result from a failure of the neural tube to close.
How can the failure of the neural tube to close differ?
The failure can occur caudally or cranially.
Cranial defect
Anencephaly
Caudal defect
Spina bifida
Explain Spina bifida
Failure of the neural tube to close caudally.
It can occur anywhere along the lenght of the spinal cord but is most common in the lumbosacral region.
Complications of Spina bifida.
Neurological deficitis occur and almost always hydrocephalus will occur.
Cognitive delay is not common.
What is hydrocephalus?
Accumulation of CSF in ventricular system.
What are the types of spina bifida?
Explain spina bifida occulta
The mildest form of spina bifida
Some of the outer part of the vertebrae have not fused completely.
Explain meningocoele.
A meningeal cyst composing of CSF. There is no neural tissue in this cyst and only CSF.
This is still a rather mild form of spina bifida as the neural tissue is still somewhat protected.
Explain myelomeningocoele.
The most severe form of spina bifida with the most severe complications. The meninges and nerves (neural tissue) protrudes out in the cyst and will be damaged.
What is anencephaly?
Failure of neural tube to close cranially.
There will be absence of cranial structures and is incompatible with life.
What is rachischisis?
Failure of neural fold to elevate and therefore incompatible with life.
Diagnosis of neural tube defects.
Raised maternal serum alpha-fetoprotein
Ultrasound
Prevention of neural tube defects.
Folic acid pre-conceptually and then for the first trimester.
This reduces incidence by 70%
What does the neuroectoderm tube form caudally?
The spinal cord
Briefly explain the development of the spinal cord.
At 3rd motnh the spinal cord is the same length as the vertebral column but then the vertebral column will start to grow faster and the spinal roots must elongate in order to exit their intervertbral foramen.
This forms the cauda equina.
What does the prosencephalon (forebrain) develop into?
Telencephalon -> cerebral hemispheres
and
diencephalon -> thalamus
What does the mesencephalon develop into?
Mesencephalon -> midbrain
What does the rhombencephalon (hindbrain) develop into?
Metencephalon -> pons and cerebellum
Myelencephalon -> medulla oblongata
Why are the flexures important?
Because growth and development at cranial neural tube exceeds the available space linearly so it must start to fold up.
This gives a cervical flexure and a cephalic flexure.
Why might hydrocephalus occur?
Can occur in spina bifida (in this case it is treated by a shunt)
Can also occur when there is obstruction of the ventricular system e.g. tumour or infection.
Most commonly in cerebral aqueduct.
What are the alar plates of the neural tube?
Dorsal plates seperated from the ventral plates by sulcus limitans.
What are the basal plates of the neural tube?
Ventral plates separated from the dorsal plates by sulcus limitans.
Functions of the alar plates.
Sensory
Functions of the basal plates
Motor
What are the neural crests?
Cells of the lateral border of the neuroectoderm tube.
These will become displaced and enter the mesoderm and undergo epithelial to mesenchymal transition.
Give examples of neural crest cell derivatives.
Give an example of what neural crest cell migration is vulnerable against.
Alcohol
What is Hirschsprung’s disease?
Aganglionic megacolon where one structure is affected in neural crest cell migration.
It is the absence of ganglions in segment of bowel.
What is DiGeorge syndrome?
Thyroid deficiency, immunodeficciency secondary to thymus defect, cardiac defects and abnormal facies due to multiple structures being affected by defects of neural crest cell migration.
