L02: Development of the CNS Flashcards
When do the first neurones form after gestation?
22-26 days
Describe the prenatal processes of brain development
22-26 days: first neurones born 6 wks: cortical neurones migrate 9 wks: midbrain expands 12 wks: cerebellum visible 6-9 mths: most major nerve tracts formed
Which germ layer forms the nervous system?
Ectoderm
What is neurulation & when does it occur?
Formation of neural plate & folding of neural tube due to induction by notochord
Occurs 3 weeks post conception
How does the neural tube fold?
Notochord & mesoderm secretes molecules forming gradient & cells at diff gradients undergo diff changes
What does the neural tube & crest cells form?
Neural tube - all of CNS
Neural crest cells - neurones w cell bodies in PNS e.g. sensory neurones, Schwann cells, autonomic post ganglionic neurones
What can failure of neural tube closure cause?
Anteriorly - anencephaly
Posteriorly - spina bifida
How may failure of neural tube closure occur?
Lack of folic acid - needed for cell division & formation of DNA for developing neurones
Gene defects - mutant proteins may prevent neural induction
How does cortical layering occur?
- Proliferation - occurs in innermost layer of neural tube (ventricular zone)
- Migration - radial glia provide scaffolding for migration of post mitotic immature neurones outwards
- Differentiation - immature neurones differentiate at their final destination to become specialised
What could cause a fault in proliferation of cortical neurones? What might this cause?
Zika virus affects proliferative genes —> microcephaly
What happens to radial glia in adulthood?
Mostly dies off
What are some, migration abnormalities of cortical neurones?
Cortical dysgenesis - most extreme = lissencephaly: smooth cortex w no sulci/gyrae & disorganised layers
What are axon growth cones?
Detect chemoattractants e.g.netrin, ephrin for axon growth
Axons grow together forming white matter tracts via protein based cell adhesion molecules
Are all synapses initially made, kept?
No - some removed to prevent inappropriate connections
Done via apoptosis not necrosis & is controlled by gene expression
Examples of pathological loss of synaptic connections?
Alzheimer’s, Parkinson’s
How does anterior-posterior patterning occur in the brain?
Signals for anterior polarity = dickkopff, noggin + requires retenoic acid (metabolite of vitamin A)
High expression in forebrain structures, low in hindbrain structures
Rostral end of neural wall forms all of brain & ventricles
How can vitamin A be teratogenic?
Too much vitamin A —> to much signalling for anterior polarity
Can cause miscarriage
How does dorsal-ventral patterning occur?
Sonic hedgehog protein expressed ventrally —> formation of cranial nerve motor neurones, dopaminergic & seratonergic neurones
Describe how the brain develops after birth
Neurone proliferation complete after 1 year
Myelination 50% complete at 18 months
No of synapses increase until 3 yrs
Brain is mature in structure at age 20 but dynamic processes continue beyond
What does the forebrain develop from embryologically? What does it then consist of?
Forms from telencephalon & diencephalon Forms cerebrum (telen) + thalamus/hypothalamus (dien)
