L02: Development of the CNS

Question 1

When do the first neurones form after gestation?

Answer 1

22-26 days

Question 2

Describe the prenatal processes of brain development

Answer 2

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

Question 3

Which germ layer forms the nervous system?

Answer 3

Ectoderm

Question 4

What is neurulation & when does it occur?

Answer 4

Formation of neural plate & folding of neural tube due to induction by notochord
Occurs 3 weeks post conception

Question 5

How does the neural tube fold?

Answer 5

Notochord & mesoderm secretes molecules forming gradient & cells at diff gradients undergo diff changes

Question 6

What does the neural tube & crest cells form?

Answer 6

Neural tube - all of CNS
Neural crest cells - neurones w cell bodies in PNS e.g. sensory neurones, Schwann cells, autonomic post ganglionic neurones

Question 7

What can failure of neural tube closure cause?

Answer 7

Anteriorly - anencephaly

Posteriorly - spina bifida

Question 8

How may failure of neural tube closure occur?

Answer 8

Lack of folic acid - needed for cell division & formation of DNA for developing neurones
Gene defects - mutant proteins may prevent neural induction

Question 9

How does cortical layering occur?

Answer 9

1. Proliferation - occurs in innermost layer of neural tube (ventricular zone)
2. Migration - radial glia provide scaffolding for migration of post mitotic immature neurones outwards
3. Differentiation - immature neurones differentiate at their final destination to become specialised

Question 10

What could cause a fault in proliferation of cortical neurones? What might this cause?

Answer 10

Zika virus affects proliferative genes —> microcephaly

Question 11

What happens to radial glia in adulthood?

Answer 11

Mostly dies off

Question 12

What are some, migration abnormalities of cortical neurones?

Answer 12

Cortical dysgenesis - most extreme = lissencephaly: smooth cortex w no sulci/gyrae & disorganised layers

Question 13

What are axon growth cones?

Answer 13

Detect chemoattractants e.g.netrin, ephrin for axon growth

Axons grow together forming white matter tracts via protein based cell adhesion molecules

Question 14

Are all synapses initially made, kept?

Answer 14

No - some removed to prevent inappropriate connections

Done via apoptosis not necrosis & is controlled by gene expression

Question 15

Examples of pathological loss of synaptic connections?

Answer 15

Alzheimer’s, Parkinson’s

Question 16

How does anterior-posterior patterning occur in the brain?

Answer 16

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

Question 17

How can vitamin A be teratogenic?

Answer 17

Too much vitamin A —> to much signalling for anterior polarity
Can cause miscarriage

Question 18

How does dorsal-ventral patterning occur?

Answer 18

Sonic hedgehog protein expressed ventrally —> formation of cranial nerve motor neurones, dopaminergic & seratonergic neurones

Question 19

Describe how the brain develops after birth

Answer 19

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

Question 20

What does the forebrain develop from embryologically? What does it then consist of?

Answer 20

Forms from telencephalon & diencephalon 
Forms cerebrum (telen) + thalamus/hypothalamus (dien)