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Semester 3 > Case 1: Neurodevelopment > Flashcards

Case 1: Neurodevelopment Flashcards

1
Q

What causes the neural plate to form and at what date

A

We start at the end of the second week (day 15-17), the notocord starts secreting grown factor which tells the ectoderm to proliferate, as it starts proliferating it forms the neural plate at day 17

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2
Q

What day does neural plate form

A

17

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3
Q

Next step after neural plate formation

A

Central part of the neural plate starts to sink and the edges comes together forming the neural folds and neural groove

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4
Q

When does the neural folds and neural groove start to form

A

Day 18

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5
Q

What happens after neural folds and neural groove starts forming

A

The ectoderm cells start to proliferate and specialized into neural crest cells, the neural folds then connect and the tube is created which sinks and goes beneath the ectoderm forming the neural tube with the neural crest cells forming above and the notochord under

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6
Q

What day do you completely form the neural tube

A

Day 21

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7
Q

What is the hole of the neural tube at the cranial part called

A

The anterior neuropore

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8
Q

What is the hole of the neural tube in the caudal part called

A

Posterior neuropore

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9
Q

What is the anterior and posterior part of the neural tube called

A

Anterior = cranial
Posterior = caudal

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10
Q

What day does the posterior neuropore close

A

28 (a week after the neural tube is fully formed)

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11
Q

What day does the anterior neuropore close

A

25 (3 days before posterior neuropore)

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12
Q

What does the cranial end of the neural tube form into (primary ones)

A
  • Prosencephalon
  • Mesencephalon
  • Rhombencephalon
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13
Q

What does the Prosencephalon form and then what does that form

A

Prosencephalon forms:
- Telencephalon which forms cerebrum (week 5 then week 6 for cerebrum)
- Diencephalon which forms thalamus, epithalmus and hypothalamus
(week 5 then 6 for those structures)

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14
Q

What day/week do the secondary brain vesicles start forming

A

Week 5

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15
Q

What day/week do the tertiary brain vesicles start forming

A

Week 6

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16
Q

What does the mesencephalon form into

A

Stays as the mesencepahlon then becomes the Midbrain

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17
Q

What does the Rhombencephalon form into

A

Rhombencephalon forms:
- Metencephalon which forms pons and cerebellum
- Myelencephalon which forms medulla oblongata

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18
Q

What do neural crest cells form

A
  • Melanocytes for the skin colour
  • Forms PNS
  • Pia mater and arachnoid mater
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19
Q

What are the 3 zones of the neural tube

A
  • Neuroepithelial or ventricular zone
  • Mantle zone
  • Marginal zone
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20
Q

What does the marginal layer contain and what do they eventually form

A

Contains axons of the neurons which will eventually form the white matter and become myelinated, also forms outer layer of cerebral context in the anterior side.

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21
Q

What does the Mantle layer consist of and what does it eventually form

A

Contains newly formed neurons (mature neuroblasts) that have migrated from the neuroepithelial layers, it forms the alar and basal plate which eventually form the dorsal and ventral grey matter

Also forms parts of the brain like the basal ganglia, cerebrum etc

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22
Q

What does the neuroepithelial zone or layer consist and what does it lead to

A

It’s the layer adjacent to the lumen of the neural tube which eventually form the ventricles in the brain, contain neuroepithelial cells which are stem like cells that are highly proliferative, these cells eventually divide to produce neural progenitor cells (NPCs) which then give rise to neuroblasts (immature ones here) and glial cells which form different cells (different flash card), as neuroblasts develop they begin to migrate to the next layer (mantle layer)

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23
Q

What do neural progenitor cells give rise to

A
  • Neuroblasts which eventually form neurons
  • Glial cells which form:
  • astrocytes (main blood brain barrier)
  • microglia (immune cells for CNS)
  • ependymal cells (produce CSF)
  • oligodendrocytes (produce myelin for CNS)
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24
Q

What is formed at the dorsal aspect of the neural tube

A

Alar plate

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25
Q

What is formed at the ventral aspect of the neural tube

A

Basal plate

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26
Q

Describe the dorsoventral axis of the neural tube and what it leads to the development of

A

Two different morphogenes are released:
- Dorsally BMP (bone morphogenetic protein) is released which leads to the development of sensory neurons
- Ventrally SHH (sonic hedgehog) is released which leads to the development of motor neurons

Sensory/dorsal neurons are formed because of the high levels of BMP and low levels of SHH and vice versa for the motor/ventral neurons

27
Q

What is a deficit of SHH (sonic hedgehog lead to?)

A

Holoprosencephaly which is where the forebrain fails to divide into 2

28
Q

What secrets SHH

A

Notochord

29
Q

What secretes BMP

A

Initially secreted by ectoderm later secreted by alar plate

30
Q

Explain the locations of the neural roof and floor

A

Neural roof is dorsal and neural floor is ventral

31
Q

Explain the antero-posterior axis of neural tube and what is secreted

A

Anterior aspect forms the brain and posterior forms spinal cord, two morphogens released are FGF (fibroblast growth factor) and retinoic acid. FGF is released most posteriorly and leads to spinal cord identity, retinoic acid is released more anteriorly but still quite posterior so high levels also lead to spinal cord identity. At the cranial end there is a low amount of FGF and retinoic acid so you get brain identity

32
Q

Two morphogens released in antero-posterior axis and their locations

A
  • FGF (fibroblast growth factor) - released most posteriorly
  • Retinoic acid - released more anteriorly to FGF
33
Q

What defects do you get when anterior neuropore fails to close

A
  • Anencephaly: baby is born without parts of its brain and skull, incompatible with life
  • Encephalocele: sac-like protrusion or projection of the brains and its membranes through an opening of the skull
  • Craniorachischisis: neural tube remains open, incompatible with life
34
Q

What conditions do you get when the posterior neuropore doesn’t close

A

Spina bifida, 3 types:
- Spina Bifida occulta
- Spina Bifida opperta
- Meningocele
- Myelomeningocele

35
Q

Spina Bifida occulta

A

Incomplete closure of the vertebrae, has a tuft of hair over the area because CSF is rich in nutrients and causes hair growth

36
Q

Meningocele

A

Type of Spina Bifida (Opperta), it’s when the meninges protrude outside the deficit alongside CSF, this contains no nerves and the spinal cord remians undamaged

37
Q

Myelomeningocele

A

Type of Spina Bifida (Spina Bifida Opperta), it’s where the meninges and part of the spinal cord protrude out of the defect resulting in severe disability

38
Q

Type 1 Chiari malformation

A

Most commonly observed typed in children, it is when the lower part of the cerebellum (the cerebellar tonsils) but not the brain stem extends into the foramen magnum

39
Q

Type 2 Chiari malformation

A

Only seen in children born with spinal Bifida, during fetal development the spinal bifida leads to loss of CSF into the defect, this causes a suction effect of the developing hindbrain (cerebellum and brainstem) causing them to extend into the foramen magnum

40
Q

Type 3 Chiari malformation

A

Most serious form of chiari malformation, it is when there is a herniation or pertrusion of the cerebellum and brain stem through the foramen magnum and INTO the spinal cord, crushing it and causing severe neurological defects

41
Q

Type 4 Chiari malformation

A

Incomplete or underdeveloped cerebellum

42
Q

Chiari malformation complications/associations

A
  • Hydrocephalus
  • Syringomyelia
  • Tethered cord syndrome
43
Q

Hydrocephalus

A

Occurs because the Chiari malformation is blocking the CSF from leaving the brain causing its buildup in the ventricles and brain, treatment is using a shunt to drain the CSF into another area of the body, usually the stomach.

44
Q

Syringomyelia

A

Caused my chiari malformation and is when a cavity or cyst called a syrinx forms within the spinal column, as the syrinx grows it can press in the nerves and cause pain, weakness and stiffness

45
Q

Tethered cord syndrome

A

Caused by chiari malformation and here the spinal cord attaches to the spine and causes the spinal cord to stretch, this causes serious nerve and muscle damage in lower body

46
Q

How to prevent neural tube defects

A

400 micrograms or 4 grams of folic acid a day 3 months before pregnancy/conception and 3 months into pregnancy

47
Q

How much should women with high risk of NTD take

A

5g daily

48
Q

Presentation of hydrocephalus

A
  • Sun-setting eyes in babies due to pressure of hydrocephalus on CN 3, 4 and 6
  • Infants my have bulging anterior fontanelle (soft spot in skull) and unusually large heads
49
Q

Does folic acid help with hydrocephalus

A

No but folate does

50
Q

Difference between folate and folic acid

A

Folate has a methyl group and is the natural form of vitamin B9 found in foods like leafy green vegetables, legumes, fruits etc. folic acid doesn’t have this methyl group and is also a synthetic version of vitamin B9

51
Q

What is folate also known as (name wise and vitamin wise)

A

5-methyltetrahydrofolate and is also known as vitamin B9

52
Q

Is CSF important

A

Yes CSF is made by ependymal cells in the choroid plexus which goes into the subarachnoid space and is very important for cerebral development

53
Q

What high levels of protein are found in cases of open spinal defect

A

Alpha-feto protein (AFP) in the mothers blood

54
Q

When is the best time to do an ultrasound to screen for Spina Bifida and why

A

Between 18-22 weeks as that is when you can see the banana and lemon sign

55
Q

What is Spina Bifida also associated with

A

Trisomy 18

56
Q

What is the lemon sign

A

It is when there is scalloping of the frontal bones causing the front of the head to look like a lemon, it is commonly associated with chiari malformation type 2 as the pulling of the hindbrain through the foramen magnum causes a downward displacement causing the frontal region to curve inward leading to the lemons sign

57
Q

What is the banana sign

A

Associated with Spina Bifida and chiari type 2 malformation, it is caused by the displacement of the posterior fossae contents such as the cerebellum and brain stem (cause of type 2 CM) and also potentially spinal cord tethering (as the pulling of the spinal cord down can cause traction on the cerebellum and brain stem). This ultimately leads the cerebellum to have a banana shape on the ultrasound called the banana sign

58
Q

When is the best time to see the banana and lemon sign and when do they disappear

A

Best seen week 18-22 on a ultrasound and usually disappears on week 24+ (6 months plus)

59
Q

Why do the banana sign and lemon sign disappear after 24 weeks

A
  • The lemon sign disappears because as the pregnancy progress the fetal brain grows and intracranial pressure normalizes
  • The banana sign disappears because as the fetal brain grows through cerebellum may expand and adapt, reducing the prominence of the banana shape
60
Q

What does the endoderm form

A

Lung cells (alveolar cells)
Thyroid cells
Digestive cells

61
Q

What does the mesoderm form

A

Cardiac muscle cells
Skeletal muscle cells
Tubules of kidney
RBCs
Smooth muscle cells in gut

62
Q

What does the ectoderm form

A

Skin cells of the epidermis
Neurons of the brain
Pigment cells (melanocytes)

63
Q

Where do neural progenitor cells proliferate and divide at and why

A

The NPC divide at the apical surface, an apical surface refers to the surface of an epithelial cell that faces outwards towards a lumen, because NPCs are located in the neuroepithelial zone of the neural tube near the neural canal the NPC divide and proliferate at that apical surface.

64
Q

What does the neural crest cells form

A

Satellite cells
Schwaan cells
Cartilage and bone
Etc

Semester 3 (13 decks)

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