Development and Anomalies of Development of the CNS Flashcards Preview

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1
Q

List 5 key events that occur in prenatal development of the brain.

For each event, give an approximation of the time at which they occur after conception.

A

3 weeks: First neurones are born.

6 weeks: Cortical neurones begin to migrate.

9 weeks: Midbrain expands.

12 weeks: Cerebellum is visible.

6-9 months: Most major nerve tracts formed.

2
Q

List 5 key events that occur in postnatal development of the brain.

For each event, give an approximation of the time at which they occur after conception.

A

12 months: Majority of proliferation is complete.

18 months: Myelination is 50% complete.

<3 years: Number of synapses increases.

> 3 years: Number of synapses begins to decline in a process known as pruning.

20 years: Brain is mature in gross structure.

3
Q

What is gastrulation?

What is a gastrula?

A
  • The transformation of a blastula into a gastrula.

- A gastrula is a polarised ball of stem cells consisting of 3 layers (the endoderm, mesoderm and ectoderm).

4
Q

What are the fates of the layers of a gastrula?

A
  • The endoderm is the precursor for viscera.
  • The mesoderm is the precursor for musculoskeletal systems.
  • The ectoderm is the precursor for the nervous system and skin.
5
Q

What is the neural plate?

A

The section of the ectoderm from which the nervous system is formed.

6
Q

What is neural induction?

On which embryological structures does neural induction rely?

A
  • The process by which embryonic cells in the ectoderm acquire a fate to form the neural plate rather than give rise to other structures such as the skin.
  • Neural induction relies on both the ectoderm and the notochord.
7
Q

What is neurulation?

When does neurulation begin?

A
  • The transformation of the neural plate into the neural tube by folding, invaginating and closing.
  • This occurs at 3 weeks after conception.
8
Q

What is the neural crest?

From which cells does the neural crest originate?

A
  • Patches of cells adjacent to the neural tube that appear after neurulation.
  • These are the cells that were on the boundary that separated the neural plate from the rest of the ectoderm before neurulation.
9
Q

What is the fate of the neural crest?

A

The neural crest will form:

1 - All neurones with cell bodies in the peripheral nervous system.

2 - All Schwann cells.

10
Q

In which direction does the closure of the neural tube (after invagination of the neural plate) occur during neurulation?

A

From posterior to anterior.

11
Q

List 2 defects that arise from defective closure of the neural tube.

For each defect, state whether the defect is on the anterior or posterior side of the neural tube.

A

1 - Anencephaly (anterior).

2 - Spina bifida (posterior).

12
Q

Define anencephaly.

A

Absence of a major portion of the brain.

13
Q

Why is folic acid important for foetal development?

A

Because folic acid is required for nucleic acid production, and therefore cell division, which occurs very frequently during foetal development.

14
Q

Define rostral and caudal.

A
  • Rostral refers to the anterior aspect of the head.

- Caudal refers to the posterior aspect of the head.

15
Q

What determines anterior-posterior and dorsal-ventral patterning of the neural tube to enable cells to function in the correct 3D location?

A
  • Genes produce signals for polarity, which are secreted and interact with cell surfaces.
  • E.g. The dickkopf and noggin genes produce signals for anterior expression. Cells expressing these genes will therefore be found in the forebrain.
  • E.g. The sonic hedgehog gene produces signals for ventral expression.
16
Q

List 3 cells expressed by ventral neural tissue.

A

1 - Cranial nerves.

2 - Dopaminergic neurones.

3 - Serotonergic neurones.

17
Q

Why is vitamin A contraindicated with pregnancy?

A

Because vitamin A can disrupt anterior-posterior patterning of the neural tube, leading to poor forebrain development.

18
Q

When and where are cortical neuroblasts formed?

A
  • From 5-20 weeks after conception.

- In the ventricular zone which lines the inner neural tube.

19
Q

Which genes are responsible for the proliferation of cortical neuroblasts?

A

Uniquely human genes.

20
Q

What might result from an abnormality in cortical neuroblast proliferation?

What might cause such an abnormality?

A
  • Microcephaly.

- Zika virus might impair neuroblast proliferation.

21
Q

What determines the organisation of cells within the cortex of the brain once polarity has been established?

A

Inside-out layering:

1 - Radial glia span the length of the cortical plate (the area that will form the cortex), giving them a spoke-like radial appearance.

2 - Radial glia form scaffolding across the cortical plate.

3 - Cortical neuroblasts are formed at the ventricular zone, which lies beneath the cortical plate.

4 - The first layer of cortical neuroblasts begin to migrate up the scaffolding of the cortical plate, but only migrate a short distance before stopping.

5 - Subsequent layers of cortical neuroblasts migrate further than previous cortical neuroblasts, forming additional layers from inside to out.

22
Q

What group of syndromes can arise from abnormalities of cortical neuroblast migration?

A

Cortical dysgenesis.

23
Q

What is lissencephaly?

A

The formation of a smooth cortex due to disorganised layering and deficiencies in neurone production.

24
Q

List 2 chemoattractants / chemorepellents that are involved in axon guidance.

A

1 - Netrin.

2 - Ephrin.

25
Q

Define growth cone.

A

The structure at the tip of a growing axon that receives signals for axonal guidance.

26
Q

Define fasciculation.

Describe the process of fasciculation.

A
  • The formation of fascicles in the developing brain, which form white matter tracts in the adult brain.

1 - Fascicles form when multiple axons grow together in the same direction by adhering axons with that of a lead neurone. Adhesion of axons occurs via cell adhesion molecules (CAMs).

2 - The lead neurone’s growth cone guides axonal growth for all neurones adhered to it.

3 - Neurones that grow after the development of fascicles also follow the path of the tract.

27
Q

Give an example of a neurotrophic factor involved in synaptogenesis.

A

Nerve growth factor.

28
Q

What process might be deficient in autism?

A

Pruning.

29
Q

What process accompanies the loss of synapses seen with pruning?

A

Organised apoptosis (not necrosis).

30
Q

List 6 conditions that are caused by neurodevelopmental abnormalities.

A

1 - Autism.

2 - Schizophrenia.

3 - Cerebral palsy.

4 - Cerebellar ataxia.

5 - Epilepsy.

6 - Dyslexia.