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Embryology > Neurulation & Embryonic Folding > Flashcards

Neurulation & Embryonic Folding Flashcards

1
Q

What happens as the primitive streak regresses?

A

The primitive node lays down the notochord

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2
Q

How is neurulation initiated?

What is this process called?

A

By signals from the notochord that cause the overlying ectoderm to thicken and form the neural plate

This is induction

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3
Q

What does the ectoderm become once it has thickened?

What happens to it as it thickens?

A

The neuroectoderm

As the ectoderm thickens, the lateral edges elevate to form neural folds

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4
Q

What happens when the neural folds elevate?

A

They meet in the midline and fuse together to form the neural tube

The neural tube goes on to form the spinal cord and the brain

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5
Q

On which day do the neural folds begin to elevate?

A

day 19

They are almost ready to fuse together on day 20

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6
Q

When the neural folds fuse, in which regions do they not fuse?

A

They fuse along the entirety of their length to form the neural tube

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7
Q

Where does fusion of the neural folds commence?

A

Fusion of the neural fold begins in the cervical (neck) region of the embryo and continues cranially and caudally

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8
Q

What does the tube separate from as the neural folds fuse?

A

The neural tube separates from the surface ectoderm

This will go on to form the epidermis of the skin

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9
Q

By which day has fusion of the neural folds in the midline completed?

A

Fusion of neural folds in the midline to form the neural tube is complete by day 22

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10
Q

What are the openings at the top and bottom of the neural tube?

A

The anterior and posterior neuropores

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11
Q

On which days to the anterior and posterior neuropores fuse?

A

The anterior neuropore fuses on day 25

The posterior neuropore fuses on day 28

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12
Q

What will the cranial and caudal ends of the neural tube form?

A

The cranial end will form the brain

The caudal end will form the spinal cord

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13
Q

When does anencephaly occur?

A

When the anterior neuropore fails to fuse

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14
Q

What happens in anencephaly?

A

There are no cerebral hemispheres (forebrain) in the brain, but there is still a brainstem

The brainstem is usually exposed

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15
Q

What happens to a baby that is born with anencephaly?

A

It is usually a stillbirth or the newborn dies a few hours after birth

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16
Q

Why may a baby with anencephaly rarely be able to survive for a few years?

A

The brainstem controls the heart, lungs and some reflexes

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17
Q

What is rachischisis caused by?

A

Failure of the posterior neuropore to fuse

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18
Q

What is rachischisis?

A

The spinal cord does not form properly, leading to paralysis

The open neural tube also prevents the formation of vertebrae leading to spina bifida

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19
Q

What is different about the neural tube in rachischisis?

A

The neural tissue forms a flat plate, rather than a tube

This plate is exposed at birth so there is a high risk of infection

20
Q

What types of defects are anencephaly, rachischisis and spina bifida?

A

neural tube defects

21
Q

Why is spina bifida classed as a neural tube defect?

A

The neural tube is correctly formed

But it is caused by abnormal induction of the sclerotome by the notochord

22
Q

By how much and why can folic acid reduce neural tube defects?

A

Folic acid reduces neural tube defects by 50-70%

It is important for correct neurulation and development of the CNS

23
Q

What happens to cells as the neural folds elevate and fuse?

A

Cells at the lateral edge separate from the neural tube

These are neural crest cells

24
Q

What is the role of the neural crest cells?

A

They migrate laterally and ventrally and differentiate into a variety of structures throughout the body

25
Q

What happens at the same time as migration of the neural crest cells?

A

The neural tube separates from the mesoderm

26
Q

What is neurofibromatosis caused by?

A

It is a genetic condition caused by a mutation in the neurofibromin 1 gene

27
Q

What is the role of the neurofibromin 1 (NF1) gene?

A

It is a tumour suppressor gene

It prevents neural crest cells from differentiating too much

28
Q

What happens in neurofibromatosis?

A

NF1 gene is switched off leading to increased cell division

Overproliferation of neural crest cells leads to formation of benign tumours of the nervous system, skin and cranial bones

29
Q

What else is occurring at the same time as neurulation?

A

The embryo goes from being a trilaminar disc to form a three-dimensional structure

It does this through embryonic folding

30
Q

What are the 2 ways in which the embryo folds and when does this occur?

A
  1. craniocaudal folding
  2. lateral folding

This occurs during the 4th week of pregnancy

31
Q

What brings about embryonic folding?

A

Differential growth of the amniotic sac and the yolk sac

The amniotic sac grows rapidly, whilst the yolk sac remains the same size

32
Q

What is the difference between craniocaudal and lateral folding?

A

Craniocaudal folding results in the C-shape of the embryo

Lateral folding causes the edges of the trilaminar disc to come together and fuse in the midline

33
Q

What is lateral folding caused by?

A

The amniotic cavity expands very quickly

Amniotic fluid surrounds the embryo and pushes the lateral edges together so that they fuse and form the body cavity

34
Q

In which regions of the embryo does the lateral body fold?

A

everywhere except for the level of the yolk sac

35
Q

During lateral folding, what will the surface ectoderm go on to form?

A

The epidermis of the skin

outer layer of the body cavity

36
Q

After craniocaudal folding, what will the ectoderm and connecting stalk go on to form?

A

Ectoderm will form the spinal cord

The connecting stalk will form the umbilical cord

37
Q

What is the allantois and the vitelline duct?

A

The allantois is the foetal bladder

The vitelline duct is the connection between the yolk sac and the midgut

38
Q

What is the process behind craniocaudal folding?

A

The amniotic cavity gets larger and pushes the head and tail end in closer proximity

This causes the embryo to become a C-shape

39
Q

What is ectopia cordis?

A

The heart develops outside of the body

This is due to the lateral folds failing to fuse correctly in the thoracic region

40
Q

What happens if the lateral folds fail to fuse?

A

There is a gap in the anterior wall

41
Q

How many live births does ectopia cordis occur in?

A

1 in 5 million

42
Q

What is gastroschisis?

A

The intestines are outside of the body wall

This is due to the lateral folds failing to fuse in the abdominal region

43
Q

What is the only area where the lateral walls should not fuse?

A

The level of the midgut

44
Q

How many live births does gastroschisis occur in?

A

3.5 per 10,000

45
Q

What is the treatment for gastroschisis?

A

The intestines are put into an aseptic bag until there is enough space in the abdominal cavity for them to be put back

Embryology (4 decks)

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