Development of the Nervous System Flashcards
Describe the process of neuralation
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
How thick is the neural tube initially?
One cell thick
What kind of gradient is present in the development of the nervous system and which end is older?
A rostral to caudal gradient, with the rostral end being more mature
What pathologies can be produced by a failure of the neural fold closure?
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
Why are pregnant women encouraged to take folate?
Folate protects against neural tube defects
How is the neural tube segmented?
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
How are the retinae formed?
As optic vesicles budding off the diencephalon
What are the mature derivatives of the telencephalon?
Cortex, basal ganglia, hippocampus
What are the mature derivatives of the diencephalon?
Thalamus and hypothalamus
From what vesicle does the cerebellum develop?
Metencephalon (same as pons)
From what vesicle does the medulla develop?
Myelencephalon
When does neural crest formation occur and from what is it formed?
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)
List the 4 derivatives of the neural crest
PNS (including DRG, ANS ganglia, enteric ganglia and Schwann cells)
Melanocytes
Muscle cartilage and bones of the skull, jaw, face and pharynx
Dentine
What is the ventricular zone?
The ventricular surface from which all new neurons are born (due to presence of stem cells); allows generation of cortex
What is the role of the radial glial cell?
Guides migration of new neurons across the cortex
Give 2 examples of development disorders arising from mutations to genes affecting neural migration
Reelin mutation (results in decreased white matter) DCX (doublecortin gene) mutation causing lissencephaly (smooth cortical surface, few neurons in cortex)
What is fragile X syndrome?
A developmental disorder caused by mutation of the fragile X mental retardation gene (FMR1), which is involved in synaptic and dendritic development
What are the somites?
Developing muscle and bone
What is the notochord?
Becomes centre of vertebral body
What is the neural tube?
Developing spinal cord
What is the role of induction in spinal cord development?
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
What is the role of the floor plate?
Induces ventral horn motor neurons through the release of signalling molecules such as sonic hedgehog
How are interneurons induced?
Signalling cascade from notochord and then floor plate induces release of motor neuron factor from motor neurons; this induces interneuron development
How do axons initially grow?
They are “towed” into position by growth cones
What is a growth cone?
Dynamic structure of cytoskeleton
Describe the development of the visual cortex
At birth, terminals from one eye form interdigitated patches with those from the other eye
What is the effect of temporary eye closure on visual cortex development?
Deprived eye has reduced cortical representation and opened eye has increased
What is the effect of the timing of temporary eye closure on visual cortex development in a kitten?
At birth: open eye will occupy 100% of cortical area
At 2-3 weeks: weaker effect
At 6 weeks: no effect
What is the critical period for establishment of relative activity in the visual cortex for humans?
10 years
