Development

Question 1

What is neuralation?

Answer 1

• Neural plate made of neuroepithelium appears in the ectoderm.
• Plate then invaginates and folds to form the neural tube below the ectoderm.

Question 2

What is the gradient running down the neural tube?

Answer 2

• Rostral to caudal gradient in the formation of the nervous system
• Rostral is older
• Caudal younger.

Question 3

How many zones of neural fold closure are there?

Answer 3

5

Question 4

What is anacephaly a result of?

Answer 4

Failure of zone 2 neural tube to close.

Question 5

What is the most common of the neural fold closure defects?

Answer 5

Spina bifida

Question 6

How can spina bifida be prevented?

Answer 6

By taking folate during pregnancy

Question 7

How does segmentation of the neural tube begin?

Answer 7

• Rostral end of neural tube starts to swell (vesiculation) and forms 3 distinct vesicles:
  
  • Prosencephalon (forebrain)
  • Mesencephalon (midbrain)
  • Rhombencephalon (hindbrain)

Question 8

What does the prosencephalon split into?

Answer 8

Telencephalon and diencephalon

Question 9

What does the rhombencephalon split into?

Answer 9

7 vesicular segments

Question 10

How does the retina form?

Answer 10

As out-pocketings of the CNS

Question 11

What are the first two vesiculations of the rhombencephalon?

Answer 11

Metencephalon and myeloencephalon.

Question 12

What do the remaining 5 vesiculations of the rhombencephalon become?

Answer 12

Spinal cord

Question 13

What are the 3 vesicles of the 3 vesicle stage?

Answer 13

Prosencephalon (forebrain) Mesencephalon (midbrain) Rhombencephalon (hindbrain)

Question 14

What does the prosencephalon become in the 5 vesicle stage?

Answer 14

Telencephalon and diencephalon

Question 15

What does the mesencephalon become in the 5 vesicle stage?

Answer 15

Mesencephalon

Question 16

What does the rhombencephalon become in the 5 vesicle stage?

Answer 16

Metencephalon and myelencephalon

Question 17

What are the mature derivatives of the telencephalon?

Answer 17

Cortex, basal ganglia, hippocampus

Question 18

What are the mature derivatives of the diencephalon?

Answer 18

Thalamus and hypothalamus

Question 19

What are the mature derivatives of the mesencephalon?

Answer 19

Midbrain

Question 20

What are the mature derivatives of the metencephalon?

Answer 20

Pons and cerebellum

Question 21

What are the mature derivatives of the caudal neural tube?

Answer 21

Spinal cord

Question 22

What is the neural crest?

Answer 22

The thin layer of cells that migrate away from the neural tube and sits beneath the ectoderm and above the neural tube.

Question 23

What are the neural crest derivatives?

Answer 23

• Peripheral nervous system
• Melanocytes
• Muscle
• Cartilage and bone of skull, face and pharynx
• Dentine

Question 24

How is the cortex generated?

Answer 24

• The neuroepithelium adds layers to generate cortex.
• New neurons are born from stem cells at the ventricular zone.
• The cells grow on inner surface and then migrate outwards inside to outside.

Question 25

How do neurons migrate through the cortex?

Answer 25

By using radial glia as scaffolding

Question 26

What is Fragile X syndrome?

Answer 26

* Most common cause of male autism. * Mutation of fragile X mental retardation gene (FMR1) * Affects synaptic and dendritic development.

Question 27

What will result from a mutation in genes that affect migration?

Answer 27

Cortex will be malformed, leading to developmental disorders and profound mental retardation.

Question 28

What is induction?

Answer 28

Signals using ligands and receptors pass between structures or tissues, inducing a particular response.

Question 29

How do axes within the spinal cord develop?

Answer 29

* The neural tube sits on top of the notochord which releases signals (e.g. sonic hedgehog) that tell the neural tube what to do and its orientation. * It defines the floor plate of the neural tube. * The roof plate does the same thing, releasing TGF-beta, establishing the roof. * This establishes axes within the neural tube.

Question 30

How are the different groups of neurons in the spinal cord induced?

Answer 30

* The notochord releases high conc. of sonic hedgehog, incuding the floor plate. * The floor plate then releases low conc. of sonic hedgehog, inducing motoneurons. * Motoneurons then release motorneuron factor, inducing interneurons to develop. * This happens in a ventral to dorsal direction.

Question 31

What is the role of the floor plate?

Answer 31

To establish an axis in the developing spinal cord and kick-start the induction cascade for motoneurons and interneurons.

Question 32

True or false: the axon is present when the neuron first develops.

Answer 32

False. The axon is a key feature of mature neurons.

Question 33

How does the axon develop?

Answer 33

It is towed into position by the growth cone.

Question 34

What is the growth cone?

Answer 34

* A dynamic structure of the cytoskeleton which steers to its target by following diffusible and membrane bound signals such as NGF. * There is a network of signalling molecules that encourage and discourage growth into a network.

Question 35

What happens if one eye of a kitten is temporarily covered shortly after birth?

Answer 35

* It will be blind in that eye. * Everything is normal in the retina and LGN, the blindness is cortical.

Question 36

What is seen in the visual cortex of a kitten that has had one eye covered from birth?

Answer 36

The deprived eye will have greatly reduced representation in the visual cortex, with the open eye having enhanced representation.

Question 37

What will happen to cortical representation of each eye if both eyes of the kitten are covered from birth?

Answer 37

Nothing. Each eye will have 50/50 ocular dominance in the visual cortex.

Question 38

What is a critical period?

Answer 38

The period of time in which the networks for each contributing eye (or other sensory modality) is created within the brain.

Question 39

Why can frequent otitis media infections in infants lead to permanent deafness?

Answer 39

Because the relative activity of that ear will be reduced compared to the other and will therefore have a reduced representation in the cortex, as the infant is currently within the critical period for neural network development.

Question 40

Why will there be no ocular dominance (rather 50/50 distribution) column disruption if both eyes are closed from birth?

Answer 40

Because activity and cortical representation is relative, not absolute.