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BGDA Lectures > Development of ectoderm derivatives and the nervous system > Flashcards

Development of ectoderm derivatives and the nervous system Flashcards

1
Q

Why is the embryonic period important?

A

Weeks 3-8 of embryogenesis
It is when the three germ layers give rise to a range of tissues and organs. Many abnormalities also arise during this time.

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2
Q

What is the cranial blind end of the gut tube after gastrulation?

A

Oropharyngeal membrane

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3
Q

What does the oropharyngeal membrane do?

A

Breaks down in the fourth week to form the opening to the oral cavity

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4
Q

What is the caudal blind end of the gut tube after gastrulation?

A

Cloacal membrane

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5
Q

What does the cloacal membrane do?

A

Disintegrates in the seventh week to form the openings of the anus and the urinary and genital tracts

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6
Q

What is the allantois?

A

A small diverticulum formed by the posterior wall of the yolk sac when the cloacal membrane appears. Extends into the connecting stalk.

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7
Q

When does the allantois appear?

A

Around the 16th day of development

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8
Q

What is the purpose of the allantois?

A

Remains rudimentary for the most part but may be involved in abnormalities of bladder development

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9
Q

What are the 4 main derivatives of the ectodermal germ layer?

A

1) Neural plate/midplate
2) Surface/lateral ectoderm
3) Ectodermal thickenings (placodes)
4) Neural crest cells

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10
Q

What is neurulation?

A

The process whereby the neural plate forms the neural tube.

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11
Q

What are the 7 steps of neurulation?

A

1) Formation of the neural plate
2) Lengthening of the neural tube
3) Elevation of lateral edges to form neural folds
4) The depressed midregion forms the neural groove
5) Fusion of neural folds in the midline
6) Formation of neural tube
7) Closure of the neuropores

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12
Q

What day does the anterior/cranial neuropore close?

A

Day 25

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13
Q

What day does the posterior/caudal neuropore close?

A

Day 28

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14
Q

What are the two divisions of the neural tube?

A

1) Cephalic portion forms brain vesicles
2) Caudal portion forms spinal cord

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15
Q

What are the two subdivisions of the neural tube in week 3?

A

Cephalic end and caudal end

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16
Q

What are the three dilations/primary brain vesicles in the cephalic end?

A

1) Prosencephalon (forebrain)
2) Mesencephalon (midbrain)
3) Rhombencephalon (hindbrain)

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17
Q

What are the secondary vesicles formed under the prosencephalon?

A

Telencephalon and diencephalon

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18
Q

What are the secondary vesicles formed under the mesencephalon?

A

Mesencephalon remains as mesencephalon

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19
Q

What are the secondary vesicles formed under rhombencephalon?

A

Metencephalon and myelencephalon

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20
Q

What is the rhombencephalic isthmus?

A

Separates the mesencephalon from the metencephalon

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21
Q

Where is the pontine flexure?

A

Between the metencephalon and myelencephalon

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22
Q

What are brain ventricles?

A

Fluid filled spaces within the brain vesicles

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23
Q

What produces cerebrospinal fluid?

A

Choroid plexus

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24
Q

Where is the choroid plexus located?

A

Within each of the 4 brain ventricles

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25
Q

What is the structure of the wall of the recently formed neural tube?

A

Pseudostratified columnar neuroepithelium composed of neuroepithelial cells

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26
Q

What happens to the neural tube with further development?

A
  • More division of neuroepithelial cells and formation of neuroblasts.
  • Formation of mantle layer
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27
Q

What is the mantle layer?

A

A zone around the neuroepithelial layer aka the future gray matter of the spinal cord. Consists of basal plates and alar plates.

28
Q

What is the marginal layer?

A

The outermost layer of the neural tube. Derived from nerve fibres emerging from neuroblasts in the mantle layer. Forms the future white matter of the spinal cord.

29
Q

What is the developmental journey of primitive nerve cells (neuroblasts)?

A

Initially have a central process extending to the lumen –> then become apolar neuroblasts –> formation of bipolar neuroblasts –> derivation of multipolar neuroblasts

30
Q

How are glial cells formed?

A

Formed by neuroepithelial cells after production of neuroblasts ceases

31
Q

What are microglial cells (CNS macrophages)?

A

Differentiation of ependymal cells when neuroepithelial cells cease to produce neuroblasts and glia blasts. They are derived from vascular mesenchyme when blood vessels grow into the nervous system.

32
Q

Where do neural crest cells migrate from to the spinal cord?

A

1) Sensory ganglia of the spinal nerves (neuroblasts and schwann cells)
2) Autonomic neuroblasts

33
Q

How do neural tube defects occur?

A

Mostly due to the abnormal closure of the neural folds in the third and fourth weeks of development

34
Q

What are examples of neural tube defects?

A

Spina bifida (spina bifida occulta, meningocele, myelomeningocele, rachischisis) and anencephaly

35
Q

What are the three subdivisions of the brain?

A

Hindbrain, midbrain and forebrain

36
Q

What is another way to subdivide the brain?

A

1) Brain stem:
Consisting of myelencephalon, mesencephalon and pons from the metencephalon

2) Higher centres
Consisting of cerebellum and cerebral hemispheres

37
Q

What does the rhombencephalon (hindbrain) consist of?

A

Myelencephalon and metencephalon

38
Q

What does the myelencephalon give rise to?

A

Medulla oblongata (caudal portion gives rise to closed part and cephalic portion open part)

39
Q

What does the metencephalon give rise to?

A

Cerebellum and pons

40
Q

What is noteworthy about the mesencephalon (midbrain)?

A

Undergoes less change than other parts of the developing brain except for the caudal part of the hindbrain.

41
Q

What does the prosencephalon (forebrain) consist of?

A

Telencephalon and diencephalon

42
Q

What does the telencephalon form?

A

Cerebral hemispheres

43
Q

What does the diencephalon form?

A

Optic cup and stalk, pituitary, thalamus, hypothalamus and epiphysis

44
Q

What are the two plates of the diencephalon?

A

Roof plate and alar plate

45
Q

What is the roof plate?

A

Consists of a single layer of ependymal cells covered by vascular mesenchyme.

46
Q

What does the roof plate form?

A

Choroid plexus of the third ventricle and pineal body (epiphysis)

47
Q

What does the alar plates form?

A

Lateral walls of the diencephalon

48
Q

What two regions is the alar plates divided into?

A

Dorsal region (future thalamus) and ventral region (hypothalamus)

49
Q

What is the most rostral level of the brain vesicles?

A

Telencephalon

50
Q

What does the telencephalon consist of?

A

Two lateral outpocketings (cerebral hemispheres) and a median portion (lamina terminalis)

51
Q

How do the two lateral outpocketings form?

A

Develops as bilateral evaginations of the lateral wall of the prosencephalon at the beginning of the 5th week

52
Q

What do the two lateral outpocketings develop?

A

Corpus striatum from basal part of hemispheres and hippocampus from wall of hemisphere

53
Q

Why are neural crest cells sometimes referred to as the fourth germ layer?

A

They are fundamentally important and contribute to many organs and tissues

54
Q

How are neural crest cells formed?

A

1) Dissociation of cells at the lateral border or crest of the neuroectoderm from their neighbours as the neural folds elevate and fuse
2) Undergo an epithelial-to-mesenchymal transition
3) Leave the neuroectoderm by active migration and displacement to enter the underlying mesoderm

55
Q

What are the 4 functional domains and lineages of neural crest cells?

A

1) Cranial neural crest
2) Vagal neural crest
3) Trunk neural crest
4) Sacral neural crest

56
Q

What are the main NC contributions of the vagal neural crest?

A

Enteric ganglia, smooth muscle cells and cardiac septa

57
Q

What are the main NC contributions of the trunk neural crest?

A

Dorsal root ganglia, sympathetic ganglia and adrenal medulla

58
Q

What are the main NC contributions of the cranial neural crest?

A

Craniofacial skeleton, cranial ganglia, teeth and thyroid cells

59
Q

What are the main NC contributions of sacral neural crest?

A

Enteric ganglia and sympathetic ganglia

60
Q

Where do cranial neural crest cells originate from?

A

The brain and superior somites.

61
Q

What are some derivatives of cranial neural crest cells?

A

Viscerocranium, teeth, cranial connective tissues, musculature of the head and face

62
Q

What is the origin of vagal neural crest cells?

A

Somites 1-7

63
Q

What is the origin of sacral neural crest cells?

A

Somite 28 to more posteriorly

64
Q

What are the derivatives of vagal and sacral neural crest cells?

A

Enteric nervous system (parasympathetic ganglia of the gut)

65
Q
A

BGDA Lectures (38 decks)

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