Session 1 - Embryrology of the CNS Flashcards
Why is the nervous system so suspect to damage during its development?
- Due to the sheer length of time it takes to develop
How is the notocord formed?
When a solid core of pre-notochordal derived cells migrates from the primitive pit cephalically
What three things does formation of the notocord drive?
Formation of
- Midline
- The axial skeleton
- The neural tube
What is neurulation?
Process whereby the neural plate forms the neural tube
How is neurulation initiated?
When the overlying ectoderm differentiates to form the neural plate;
How does the neural plate form the neural tube?
It thickens and its lateral edges rise up, while the midline depresses (forming the neural groove).
The lateral edges approach each other at the midline to form the neural tube.
Where does fusion of the neural plate to form the neural tube begin, and in what direction does it proceed?
Begins in the cervical region and proceeds in the cranial and caudal directions.
What are neuropores?
Openings in the two ends of the neural tube.
What does a defect in fusion of neural tube form?
Neural tube defects
What does failure of the neural tube to close caudally cause?
Spina bifida
Failure to close crainially?
Anecephaly
Define spina bifida
Failure of caudal fusion of the neural tube
Where does spina bifida usually occur?
In the lumbosacral region
What deficits are usually associated with spina biffida?
- Neurological deficits
- Hydrocephalus
Why does hydrocephalus occur in spina bifida?
Lengthening of vertebral column causes the cerebellum to be pulled into the magnum foramen, cutting of the CSF
What are the two main types of spina bifida?
Spina bifida occulta
Spina bifida cystica
What is spina bifida occulta?
A defect in the vertebral arches whereby there is a lack of fusion of the vertebral arches. Cyst formation in the subarachnoid space, but no herniation of spinal cord
What is spina biffida cystica?
A severe NTD where neural tissue and/or meninges protrude through the skin to form a cyst like sac.
What is a meningocele?
If only fluid-filled meninges are in the sac in spina bifida cystica
What is a meningomyelocele?
If neural tissue AND menignes are in the cyst in spina bifida cystica
How does anencephaly occur?
failure of the cranial neuropore to close properly, resulting in an absence of brain structures, including the brain, so is incompatible with life.
What is rachischisis
- Rachischisis occurs when the neural folds do not elevate but remain as a flattened mass of neural tissue. Vertebrae do not fuse, leaving the neural tube exposed.
Give two ways neural tube defects can be detected?
Through raised serum α-fetoprotein or on USS
How can NTD be prevented?
Increased folic acid intake before and during the first trimester has been known to reduce incidence by 70%.
How does the spinal cord change during development
At three months spinal cord is same length as the vertebral column, but in an adult is much shorter
Where does the spinal cord end in the adult?
L1/L2
Where are lumbar punctures usually taken?
L3/L4
What is the area of the spine called where lumbar punctures take place?
Cauda equina
What are the three primary brain regions during neural fold formation?
- forebrain (prosencephalon)
- midbrain (mesencephalon)
- hindbrain (rhombencephalom).
What are the five secondary brain vesicles known as?
telencephalon, diencephalon, mesencephalon, metencephalon, myelencephalon.
What two secondary brain vesicles does the prosencephalon form?
Telencephalon
Dieencephalon
What secondary brain vesicles does the mesencephalon form?
Mesencephalhon
What does the rhombencephalon form?
Metencephalon and myelencephalon
Give the adult brain equivalents for these developmental pre-cursors
Telencephalon
Cerebral hemisphere
Give the adult brain equivalents for these developmental pre-cursors
Diencephalon
Thalamus
Give the adult brain equivalents for these developmental pre-cursors
Mesencephalon
Midbrain
Give the adult brain equivalents for these developmental pre-cursors
Metencephalon
Pons & Cerebellum
Give the adult brain equivalents for these developmental pre-cursors
Myelencephalon
Medulla Oblongata
Why does the brain form flexures?
Because the cranial end of the neural tube undergoes such rapid enlargement
Where are the two flexures of the brain?
Cervical flexure at the spinal cord hindbrain junction and a cephalic flexure at the meidbrain region
What is the ventricular system of the brain?
Acts as a reservoir of CSF, cushioning the brain and spinal cord within their bony cases
What are two reasons for the formation of hydrocephalus?
Can result if there is blockage of the ventricular system or impaired absorption of CSF fluid
What are the three layers of the neural tube, from inside to out?
- Neuroepithelial layer
- Intermediate layer (neuroblasts)
- Marginal layer (processes)
Where do neural crest cells come from?
Cells of the lateral border of the neuroectoderm tube become displaced and enter the mesoderm and undergo epithelial to mesenchymal transition.
What is the role of neural crest cells?
They have an input in a large number of different structures’ development, such as adrenal medulla, Schwann cells, or C cells of the thyroid gland.
Why do neural crest cells mess people up so often?
Their migration is particularly sensitive to environmental and genetic insult
Outline a disease of neural crest cells
Hirschsprung’s Disease
Hirschsprung’s Disease (or congenital aganglionic megacolon) is a disorder of the gut which is caused by the failure of the neural crest cells to migrate completely during fetal development of the intestine. The affected segment of the colon fails to relax, causing an obstruction.
