Neuro embryology Flashcards
Which layer of the trilaminar disc gives rise to the nervous system?
Ectoderm- thickens to form a neural plate
How does the notochord form and what does it do?
Migration of pre-notochordal cells into the primitive pit gives rise to the notochord in the midline. They initiate the thickening of the ectoderm to form a neural plate which will go on to form the neural tube.
How is the neural tube formed?
Folding of neural plate at day 19.
- central neural groove forms in the midline
- takes about 10 days
- elevation of the edges followed by fusion at the midline
Where do you find the future cervical region?
Where fusion of the tube begins.
Why do neural tube defects occur?
Due to defects in closure of the neuropores
When do the neuropores fuse?
Anterior = day 25 Posterior = day 28
Describe spina bifida
Failure of closure at the caudal end of the neural tube- leads to incomplete development of the vertebral arches
What are the different types of spina bifida?
Spina bifida occulta
Spina bifida cystica
Describe spina bifida cystica
NT fails to close, vertebral arched fail to form and the neural tissue is exposed- spinal cord and neural tissue can herniate into back region, causing a cyst- usually accompanied by hydrocephalus, does not cause it though
Where can spina bifida cystica occur?
Anywhere along the spinal cord- most common in the lumbosacral region
Why can cognitive delays occur in spina bifida cystica?
Due to hydrocephalus hat sometimes accompanies SB cystica- not directly due to spina bifida
Describe meningocoele
Meninges herniate through the unfused regions of the spine
Describe myelomeningocoele
Spinal cord and meninges herniate though the unfused regions of the lumbar spine
Describe spina bifida occulta
Not as serious
- defect of spinous processes but meninges are mostly enclosed in vertebrae
- usually asymptomatic
Describe hydrocephalus
Accumulation of CSF in ventricle or cavities of the brain Leads to: increase ICP head enlargement convulsion tunnel vision mental disability
Describe anencphaly
NTD neural tube fails to close cranially leading to tissue degeneration and little/no formation of higher brain centres
What are the characteristics of anencephaly?
Complete absence of cranial structures- condition is incompatible with life- babies that make it to term will often be stillborn
Describe rachischisis
Failure of neural fold elevation. Most severe NTD
- splayed nervous tissue
- incompatible with life
- can occur with anencephaly
How can NTD be diagnosed?
Raise serum alpha-fetoprotein
- NTD and failure of closure of abdominal structures
Ultrasound
What can reduce the incidence of NTDs?
Mother taking folic acid supplements
- 3 months pre-conception and for the 1st trimester
What does the neural tube give rise to?
Spinal cord
Describe how the vertebral column and spinal cord develop together
3 months - same length
Spinal cord stops growing at this point
VC grows longer and faster than the SC
Roots of nerve below L1/L2 must elongate so they can exit through their intervertebral foramen
Gives rise to the cauda equina
Pia mater surrounding spinal cord projects down and attaches the conus medullaris to the back of the coccyx
Called the filum terminale and stabilises the spinal cord.
Where do lumbar punctures usually occur?
At or below L4/L5
Will not damage the spinal cord
Conus medullaris terminates at L2
Lumbar fluid is drawn form the lumbar cistern
What does the lumbar cistern contain?
Filum terminales
Nerve roots of cauda equina
