Development of the Nervous System

Question 1

Describe the process of neuralation

Answer 1

The neural plate develops as specialised epithelial cells of the ectoderm; this plate then invaginates, forming a deep groove; the lips of the invagination come together (in the middle initially, leaving both ends open) and five “zippering shut” events occur to form a tubular structure; this structure is now separate from the ectoderm and lies directly below it and immediately above the notochord

Question 2

How thick is the neural tube initially?

Answer 2

One cell thick

Question 3

What kind of gradient is present in the development of the nervous system and which end is older?

Answer 3

A rostral to caudal gradient, with the rostral end being more mature

Question 4

What pathologies can be produced by a failure of the neural fold closure?

Answer 4

If the 2nd “zippering shut” event fails, anencephaly will result, with no development occurring above the level of the eyes (no brain, cortex, skull)
If the 5th event fails, this will result in spina bifida

Question 5

Why are pregnant women encouraged to take folate?

Answer 5

Folate protects against neural tube defects

Question 6

How is the neural tube segmented?

Answer 6

Rostral end of tube swells to form 3 distinct vesicles, which then further subdivide:
1) Prosencephalon (forebrain; splits into telencephalon and diencephalon
2) Mesencephalon (midbrain)
3) Rhombencephalon (hindbrain; splits into 7 segments, then into metencephalon or pons, and myeloencephalon, or medulla)
The rest of the intact neural tube becomes the spinal cord

Question 7

How are the retinae formed?

Answer 7

As optic vesicles budding off the diencephalon

Question 8

What are the mature derivatives of the telencephalon?

Answer 8

Cortex, basal ganglia, hippocampus

Question 9

What are the mature derivatives of the diencephalon?

Answer 9

Thalamus and hypothalamus

Question 10

From what vesicle does the cerebellum develop?

Answer 10

Metencephalon (same as pons)

Question 11

From what vesicle does the medulla develop?

Answer 11

Myelencephalon

Question 12

When does neural crest formation occur and from what is it formed?

Answer 12

In parallel with neural tube formation, the cells at the top of the neural tube form the neural crest and break free from the tube (still sitting below the ectoderm)

Question 13

List the 4 derivatives of the neural crest

Answer 13

PNS (including DRG, ANS ganglia, enteric ganglia and Schwann cells)
Melanocytes
Muscle cartilage and bones of the skull, jaw, face and pharynx
Dentine

Question 14

What is the ventricular zone?

Answer 14

The ventricular surface from which all new neurons are born (due to presence of stem cells); allows generation of cortex

Question 15

What is the role of the radial glial cell?

Answer 15

Guides migration of new neurons across the cortex

Question 16

Give 2 examples of development disorders arising from mutations to genes affecting neural migration

Answer 16

Reelin mutation (results in decreased white matter)
DCX (doublecortin gene) mutation causing lissencephaly (smooth cortical surface, few neurons in cortex)

Question 17

What is fragile X syndrome?

Answer 17

A developmental disorder caused by mutation of the fragile X mental retardation gene (FMR1), which is involved in synaptic and dendritic development

Question 18

What are the somites?

Answer 18

Developing muscle and bone

Question 19

What is the notochord?

Answer 19

Becomes centre of vertebral body

Question 20

What is the neural tube?

Answer 20

Developing spinal cord

Question 21

What is the role of induction in spinal cord development?

Answer 21

Notochord releases a verity of signalling molecules (including high concentrations of sonic hedgehog which induce notochord formation) which diffuse out and interact with nearby cells to induce specific responses

Question 22

What is the role of the floor plate?

Answer 22

Induces ventral horn motor neurons through the release of signalling molecules such as sonic hedgehog

Question 23

How are interneurons induced?

Answer 23

Signalling cascade from notochord and then floor plate induces release of motor neuron factor from motor neurons; this induces interneuron development

Question 24

How do axons initially grow?

Answer 24

They are “towed” into position by growth cones

Question 25

What is a growth cone?

Answer 25

Dynamic structure of cytoskeleton

Question 26

Describe the development of the visual cortex

Answer 26

At birth, terminals from one eye form interdigitated patches with those from the other eye

Question 27

What is the effect of temporary eye closure on visual cortex development?

Answer 27

Deprived eye has reduced cortical representation and opened eye has increased

Question 28

What is the effect of the timing of temporary eye closure on visual cortex development in a kitten?

Answer 28

At birth: open eye will occupy 100% of cortical area
At 2-3 weeks: weaker effect
At 6 weeks: no effect

Question 29

What is the critical period for establishment of relative activity in the visual cortex for humans?

Answer 29

10 years