Embryology 4: Neurulation & embryonic folding

Question 1

How is the neuroectoderm formed

Answer 1

Notochord induces thickening of ectoderm

Question 2

What gives rise to the neural plate

Answer 2

Neroectoderm

Question 3

How are the neuroma fold formed

Answer 3

The elevation of the lateral edges of the neural plate

Question 4

How is the neural tube formed

Answer 4

Fusion of neural folds —> begins in cervical region of embryo —> continues cranial and caudally

Question 5

When is the neuroectoderm formed

Answer 5

Day 19

Question 6

When are neural folds formed

Answer 6

Day 20

Question 7

When is neural tube formed

Answer 7

Day 22

Question 8

When does anterior Neuroptera fuse to neural tube

Answer 8

Day 25

Question 9

When does posterior Neuroptera fuse to neural tube

Answer 9

Day 28

Question 10

What will the cranial end of the neural tube form

Answer 10

Brain

Question 11

What will the caudal end of the neural tube form

Answer 11

Spinal cord

Question 12

What is anencephaly

Answer 12

Failure of anterior Neuroptera to fuse

Question 13

What happens in anencephaly

Answer 13

• forebrain doesn’t form

- brain stem present (exposed)

Question 14

What is the forebrain responsible for

Answer 14

• cognition thinking
• memory
• speech
• vision & hearing

Question 15

What is the brain stem responsible for

Answer 15

• heart
• lungs
• some reflexes

Question 16

Name diseases that may result from failure of posterior neuropore to fuse

Answer 16

• spina bifida occulta
• meningocele
• meningomyelocele
• Rachischisis

Question 17

What happens is rachischisis

Answer 17

• spinal cord doesn’t form properly —> paralysis

Question 18

Why does rachischisis cause spina bifida

Answer 18

Open neural tube prevents formation of vertebrae

Question 19

Why does rachischisis increase the risk of infection

Answer 19

Flat plate of neural tissue is exposed at birth

Question 20

What kind of defects are spina bifida, anecephaly & rachischisis

Answer 20

Neural tube defects

Question 21

What happens in spina bifida

Answer 21

Abnormal induction of the sclerotome by the notochord

Question 22

How frequent are NTDs in UK

Answer 22

1 in 1000 births

Question 23

By how much does folic acid reduce NTDs risk by

Answer 23

50-70%

Question 24

How do neural crest cells form

Answer 24

• neural folds elevate & fuse

- lateral edge cells separate from neural tube

Question 25

What do neural crest cells do after formation

Answer 25

- migrate laterally & centrally | - differentiate into a variety of structures

Question 26

Give an example of disease caused by defects in neural crest cell development

Answer 26

Neurofibromatosis

Question 27

What is neurofibromatosis

Answer 27

Genetic condition

Question 28

What causes neurofibromatosis

Answer 28

Mutation in neurofibromin 1 (NF1) gene

Question 29

What is NF1

Answer 29

Tumour suppressant

Question 30

What does NF1 do

Answer 30

Switch off neurofibromatosis —> increased cell division

Question 31

What does neurofibromatosis cause

Answer 31

Benign tumours in - nervous system - skin - cranial bones

Question 32

When does the embryo start to fold

Answer 32

During the 4th week

Question 33

What a re the two directions of folding that the embryo undergoes

Answer 33

- craniocaudal | - lateral

Question 34

Why does the embryo fold in two directions

Answer 34

- Differential growth on amniotic sac and yolk sac - amniotic grows rapidly - yolk remains same size

Question 35

What does allantois do

Answer 35

Connected to foetal bladder

Question 36

What does Vitelli next duct do

Answer 36

Connection between between yolk sac & midgut

Question 37

Example of ventral body wall defects

Answer 37

Ectopia cordis

Question 38

What happens in ectopia cordis

Answer 38

Lateral folds fail to fuse in thoracic region

Question 39

Examples of ventral body wall defects

Answer 39

Ectopia cordis Gastroschisis

Question 40

What happens in ectopia cordis

Answer 40

Lateral folds fail to fuse in thoracic region —> heart outside body

Question 41

How rare is ectopia cordis

Answer 41

1 in 5 million

Question 42

What is gastroschisis

Answer 42

- Lateral folds fail to fold in abdominal region | - intestines outside body wall

Question 43

How common is gastroschisis

Answer 43

3.5 in 10000 births