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MBD > Congenital Diseases Associated With The Central Nervous System > Flashcards

Congenital Diseases Associated With The Central Nervous System Flashcards

1
Q

What stimulates the neurulation process?

A

The notochord

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2
Q

What is the neural plate?

A
  • It is initially a flat sheet of cells located along the dorsal portion of the developing embryo in direct continuation with the epidermis, and exposed to the extraembryonic medium.
  • This sheet of cells will become a tube, and will end up being located inside the embryo.
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3
Q

What does the neural tube give rise to?

A
  • Brain
  • Spinal cord
  • Cranial and spinal nerves
  • Eyes and other sensory organs
  • Neural crest
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4
Q

When is the neural tube formed?

A

In gastrulation at week 3/4

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5
Q

What happens as the neural tube closes?

A

Becomes patterned along the dorso-ventral and rostro-caudal axis

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6
Q

What is the closing of the neural tube driven by?

A

This process is driven by secreted signalling molecules, which promote the specification of different CNS structures along each axis

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7
Q

What are defects classified according to?

A

Stage thought to be affected

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8
Q

What are the classifications of neural tube defects?

A
  • Early CNS patterning
  • Neural tube closure
  • Regional brain defects
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9
Q

What is an example of an early CNS patterning defect?

A

Holoprosencephaly (HPE)

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10
Q

What are the types of HPE’s?

A
  • Alobar HPE
  • Semilobar HPE
  • Lobar HPE
  • Microforms of HPE
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11
Q

What is Alobar HPE?

A
  • Refers to the formation of a single ventricle, and the absence of interhemispheric fissure.
  • Not only the brain, but also other CNS derivatives and face structures are affected in this from.
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12
Q

What is an example of Alobar HPE?

A

The separation of the eye field into two optic primordia does not occur, and the affected individuals also display cyclopia.

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13
Q

What is Semilobar HPE?

A

Shows partial cortical separation, rudimentary hemispheres and a single ventricle.

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14
Q

What is Lobar HPE?

A

Shows separate ventricles, but there is still incomplete frontal cortical separation.

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15
Q

What are microforms of HPE?

A
  • Some milder forms of HPE have been described, which show much milder midline defects
  • Sometimes only identifiable by a single maxillary median incisor or hypotelorism (close set eyes), and no brain malformation
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16
Q

What are Exencephaly and Anencephaly?

A
  • These conditions refer to the lack of closure in the brain region.
  • Lack of closure results in exencephaly (“brain exposed”).
  • In this condition, the brain tissue remains exposed to the amniotic cavity and eventually degenerates, resulting in anencephaly (“lack of brain”).
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17
Q

What are some examples of neural tube closure defects?

A
  • Chraniorachischsis
  • Exencephaly
  • Spina bifida
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18
Q

What is Spina Bifida?

A
  • This defect refers to the malformation of the spine and/or spinal cord, usually in the lumbar area.
  • It can be due to the failure in the closing of the neural tube during neurulation.
  • It can also be due to defective formation of the vertebrae, resulting in the spinal cord being exposed and unprotected.
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19
Q

What are the types of Spina bifida?

A

Spina bifida can be classified as occulta, meningocele and myelomeningocele

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20
Q

What are regional brain disorders?

A
  • Refers to diseases where whole elements of the CNS are missing or underdeveloped.
  • They are often related to defective rostro-caudal CNS patterning.
  • Gene-phenotype correlations are not very clear.
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21
Q

What is the difference between Spina bifida and anencephaly?

A
  • Anencephaly is when the anterior (rostral) end of the neural tube remains open
  • Spina bifida is when the posterior (caudal) end remains open
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22
Q

How many neural tube closure points are there?

A
  • Three main and two others
23
Q

Where is the first closure of the neural tube?

A

Between hindbrain and spinal cord

24
Q

Where is the second closure of the neural tube?

A

Between forebrain and midbrain

25
Q

Where is the third closure of the neural tube?

A

Most rostral portion of forebrain and only progresses posteriorly

26
Q

Where is the fourth closure of the neural tube?

A

More rostral and within the hindbrain than closure 1

27
Q

Where is the fifth closure of the neural tube?

A

Most posterior point so only progresses anteriorly

28
Q

What are the two modes of neural tube closure?

A

Primary or secondary neurulation

29
Q

What happens in primary neurulation?

A
  • Rolling up of tube
  • Closure is by fold apposition then ‘zipping up’
30
Q

What is secondary neurulation?

A

Tunneling or hollowing of tail bud

31
Q

What are the steps in primary neurulation?

A
  • Shaping
  • Folding
  • Elevation
  • Convergence
  • Closure
32
Q

What happens in the shaping step of primary neurulation?

A

Narrowing along the mediolateral axis and extend along the rostro-caudal axis

33
Q

What happens in the folding step of primary neurulation?

A

Occurs by the establishment of hinge points along the neural plate

34
Q

What is the first hinge point to appear in primary neurulation?

A

Midline hingepoint

35
Q

What happens in the elevation step of primary neurulation?

A

Lateral wings of neural plate to fold up

36
Q

What happens in the convergence step of primary neurulation?

A

More hinge points formed next to the neural crest which allows for the rounding of the plate

37
Q

What causes the cell wedging at hinge points in primary neurulation?

A

Microtubules and actin filaments

38
Q

What is Craniorachischisis?

A
  • The most severe form of neural tube defect.
  • The neural tube remains open along the whole body axis
39
Q

How does rachischisis differ from Craniorachischisis?

A

If the forebrain closes normally, the defect is then called rachischisis

40
Q

What is primary neurulation controlled by?

A

Planar cell polarity pathway

41
Q

What is convergence-extension?

A

Process of lengthening by narrowing

42
Q

What does convergence-extension require?

A

Cells to become polarised in the plane of the cell layer

43
Q

What is convergence- extension controlled by?

A

Wnt-PCP pathway

44
Q

What are the names of coreceptors necessary for signal transduction?

A

Vangl and celsr

45
Q

What does the wnt-PCP pathway lead to?

A

Regulation of transcription and regulation of the cytoskeleton

46
Q

What do mouse mutants in components of the wnt-PCP pathway show?

A

Neural tube defects:
Abnormally broad neural plate with a non-bending region

47
Q

What is cell wedging?

A

Mechanism by which the hinges on the neural plate are formed

48
Q

What is cell wedging caused by?

A

Cytoskeleton remodelling at the apical cortex

49
Q

What maintains the shape of subapical epithelial cells?

A

Lots of actin filaments that maintain the shape of cells

50
Q

What are some environmental factors that are associated with neural tube defects?

A
  • Maternal diet/obesity
  • Diabetes
  • Hypertermia
  • Teratogenic agents
51
Q

What is hypertermia?

A

Severe disease that includes high temperature in early pregnancy

52
Q

What is an example of a teratogenic agent?

A

Valproic acid

53
Q

How much folic acid does a pregnant women with no NTD history need to take?

A

0.4mg/day

54
Q

How much folic acid does a pregnant women with a NTD history need to take?

A

5mg/day

MBD (23 decks)

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