Development and Anomalies of Development of the CNS Flashcards
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.
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.
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.
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.
What is gastrulation?
What is a gastrula?
- 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).
What are the fates of the layers of a gastrula?
- 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.
What is the neural plate?
The section of the ectoderm from which the nervous system is formed.
What is neural induction?
On which embryological structures does neural induction rely?
- 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.
What is neurulation?
When does neurulation begin?
- The transformation of the neural plate into the neural tube by folding, invaginating and closing.
- This occurs at 3 weeks after conception.
What is the neural crest?
From which cells does the neural crest originate?
- 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.
What is the fate of the neural crest?
The neural crest will form:
1 - All neurones with cell bodies in the peripheral nervous system.
2 - All Schwann cells.
In which direction does the closure of the neural tube (after invagination of the neural plate) occur during neurulation?
From posterior to anterior.
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.
1 - Anencephaly (anterior).
2 - Spina bifida (posterior).
Define anencephaly.
Absence of a major portion of the brain.
Why is folic acid important for foetal development?
Because folic acid is required for nucleic acid production, and therefore cell division, which occurs very frequently during foetal development.
Define rostral and caudal.
- Rostral refers to the anterior aspect of the head.
- Caudal refers to the posterior aspect of the head.
What determines anterior-posterior and dorsal-ventral patterning of the neural tube to enable cells to function in the correct 3D location?
- 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.
