Embryology 4: Neurulation & embryonic folding Flashcards
How is the neuroectoderm formed
Notochord induces thickening of ectoderm
What gives rise to the neural plate
Neroectoderm
How are the neuroma fold formed
The elevation of the lateral edges of the neural plate
How is the neural tube formed
Fusion of neural folds —> begins in cervical region of embryo —> continues cranial and caudally
When is the neuroectoderm formed
Day 19
When are neural folds formed
Day 20
When is neural tube formed
Day 22
When does anterior Neuroptera fuse to neural tube
Day 25
When does posterior Neuroptera fuse to neural tube
Day 28
What will the cranial end of the neural tube form
Brain
What will the caudal end of the neural tube form
Spinal cord
What is anencephaly
Failure of anterior Neuroptera to fuse
What happens in anencephaly
- forebrain doesn’t form
- brain stem present (exposed)
What is the forebrain responsible for
- cognition thinking
- memory
- speech
- vision & hearing
What is the brain stem responsible for
- heart
- lungs
- some reflexes
Name diseases that may result from failure of posterior neuropore to fuse
- spina bifida occulta
- meningocele
- meningomyelocele
- Rachischisis
What happens is rachischisis
- spinal cord doesn’t form properly —> paralysis
Why does rachischisis cause spina bifida
Open neural tube prevents formation of vertebrae
Why does rachischisis increase the risk of infection
Flat plate of neural tissue is exposed at birth
What kind of defects are spina bifida, anecephaly & rachischisis
Neural tube defects
What happens in spina bifida
Abnormal induction of the sclerotome by the notochord
How frequent are NTDs in UK
1 in 1000 births
By how much does folic acid reduce NTDs risk by
50-70%
How do neural crest cells form
- neural folds elevate & fuse
- lateral edge cells separate from neural tube
What do neural crest cells do after formation
- migrate laterally & centrally
- differentiate into a variety of structures
Give an example of disease caused by defects in neural crest cell development
Neurofibromatosis
What is neurofibromatosis
Genetic condition
What causes neurofibromatosis
Mutation in neurofibromin 1 (NF1) gene
What is NF1
Tumour suppressant
What does NF1 do
Switch off neurofibromatosis —> increased cell division
What does neurofibromatosis cause
Benign tumours in
- nervous system
- skin
- cranial bones
When does the embryo start to fold
During the 4th week
What a re the two directions of folding that the embryo undergoes
- craniocaudal
- lateral
Why does the embryo fold in two directions
- Differential growth on amniotic sac and yolk sac
- amniotic grows rapidly
- yolk remains same size
What does allantois do
Connected to foetal bladder
What does Vitelli next duct do
Connection between between yolk sac & midgut
Example of ventral body wall defects
Ectopia cordis
What happens in ectopia cordis
Lateral folds fail to fuse in thoracic region
Examples of ventral body wall defects
Ectopia cordis
Gastroschisis
What happens in ectopia cordis
Lateral folds fail to fuse in thoracic region —> heart outside body
How rare is ectopia cordis
1 in 5 million
What is gastroschisis
- Lateral folds fail to fold in abdominal region
- intestines outside body wall
How common is gastroschisis
3.5 in 10000 births
