L02 - Development & 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 considerably
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
Define neuroplasticity.
Ability of the brain to form & reorganise synaptic connections throughout life
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 outcomes of the 3 layers of a gastrula?
Endoderm -> viscera
Mesoderm -> MSK
Ectoderm -> nervous system (+ skin)
What is the neural plate?
The section of ectoderm from which the nervous system is formed
What is neural induction?
The process by which embryonic cells in the ectoderm acquire a fate to form the neural plate (rather than skin) due to signals from the notochord
What is neurulation?
The transformation of the neural plate into the neural tube by folding, invaginating and closing
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
List 2 defects that arise from defective closure of the neural tube.
1 - Anteriorly = anencephaly
2 - Posteriorly = spina bifida
Why is folic acid important for foetal development?
Folic acid is required for nucleic acid production, and therefore cell division, which occurs very frequently during foetal development
What determines anterior-posterior patterning of neurones?
The dickkopf and noggin genes produce signals for anterior expression. Cells expressing these genes will therefore be found in the forebrain
What determines dorsal-ventral patterning of neurones?
The sonic hedgehog (Shh) gene produces signals for ventral expression
List 3 neurones formed by ventral expression.
1 - Motor neurones of cranial nerves
2 - Dopaminergic neurones
3 - Serotonergic neurones
Why is vitamin A contraindicated in pregnancy?
Forebrain induction relies on retinoid acid, and excessive vitamin A floods the brain with signals, and disrupts induction
How are cortical neuroblasts formed?
Proliferation of cells in the ventricular zone
What are radial glial cells?
Cells that span the cortical plate and form a scaffold to direct the migration of cortical neuroblasts
What are post-mitotic immature neurones?
Cells that have migrated up radial glia away from the ventricular zone towards the cortical plate
What happens at the final destination of immature neurones?
Differentiation -> typical cellular structure; no further divisions; differential gene activation (e.g. receptors, NTs)
What group of syndromes can arise from abnormalities of cortical neuroblast migration?
Cortical dysgenesis
What is lissencephaly?
Smooth cortex & disorganised layers
How do cortical neuroblasts migrate up the cortical plate?
Inside-out layering - there is greater cortical migration by each successive generation of cells
List 2 chemoattractants / chemorepellents that are involved in axon guidance.
1 - Netrins
2 - Ephrins
What is fasciculation?
Axons grow together as white matter bundles, mediated by CAMs
Give an example of a neurotrophic factor involved in synaptogenesis.
NGF
What process accompanies the loss of synapses seen with pruning?
Apoptosis
