Development Flashcards
What is neuralation?
- Neural plate made of neuroepithelium appears in the ectoderm.
- Plate then invaginates and folds to form the neural tube below the ectoderm.
What is the gradient running down the neural tube?
- Rostral to caudal gradient in the formation of the nervous system
- Rostral is older
- Caudal younger.
How many zones of neural fold closure are there?
5
What is anacephaly a result of?
Failure of zone 2 neural tube to close.
What is the most common of the neural fold closure defects?
Spina bifida
How can spina bifida be prevented?
By taking folate during pregnancy
How does segmentation of the neural tube begin?
- Rostral end of neural tube starts to swell (vesiculation) and forms 3 distinct vesicles:
- Prosencephalon (forebrain)
- Mesencephalon (midbrain)
- Rhombencephalon (hindbrain)
What does the prosencephalon split into?
Telencephalon and diencephalon
What does the rhombencephalon split into?
7 vesicular segments
How does the retina form?
As out-pocketings of the CNS
What are the first two vesiculations of the rhombencephalon?
Metencephalon and myeloencephalon.
What do the remaining 5 vesiculations of the rhombencephalon become?
Spinal cord
What are the 3 vesicles of the 3 vesicle stage?
Prosencephalon (forebrain) Mesencephalon (midbrain) Rhombencephalon (hindbrain)
What does the prosencephalon become in the 5 vesicle stage?
Telencephalon and diencephalon
What does the mesencephalon become in the 5 vesicle stage?
Mesencephalon
What does the rhombencephalon become in the 5 vesicle stage?
Metencephalon and myelencephalon
What are the mature derivatives of the telencephalon?
Cortex, basal ganglia, hippocampus
What are the mature derivatives of the diencephalon?
Thalamus and hypothalamus
What are the mature derivatives of the mesencephalon?
Midbrain
What are the mature derivatives of the metencephalon?
Pons and cerebellum
What are the mature derivatives of the caudal neural tube?
Spinal cord
What is the neural crest?
The thin layer of cells that migrate away from the neural tube and sits beneath the ectoderm and above the neural tube.
What are the neural crest derivatives?
- Peripheral nervous system
- Melanocytes
- Muscle
- Cartilage and bone of skull, face and pharynx
- Dentine
How is the cortex generated?
- 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.
How do neurons migrate through the cortex?
By using radial glia as scaffolding
What is Fragile X syndrome?
- Most common cause of male autism.
- Mutation of fragile X mental retardation gene (FMR1)
- Affects synaptic and dendritic development.
What will result from a mutation in genes that affect migration?
Cortex will be malformed, leading to developmental disorders and profound mental retardation.
What is induction?
Signals using ligands and receptors pass between structures or tissues, inducing a particular response.
How do axes within the spinal cord develop?
- 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.
How are the different groups of neurons in the spinal cord induced?
- 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.
What is the role of the floor plate?
To establish an axis in the developing spinal cord and kick-start the induction cascade for motoneurons and interneurons.
True or false: the axon is present when the neuron first develops.
False. The axon is a key feature of mature neurons.
How does the axon develop?
It is towed into position by the growth cone.
What is the growth cone?
- 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.
What happens if one eye of a kitten is temporarily covered shortly after birth?
- It will be blind in that eye.
- Everything is normal in the retina and LGN, the blindness is cortical.
What is seen in the visual cortex of a kitten that has had one eye covered from birth?
The deprived eye will have greatly reduced representation in the visual cortex, with the open eye having enhanced representation.
What will happen to cortical representation of each eye if both eyes of the kitten are covered from birth?
Nothing. Each eye will have 50/50 ocular dominance in the visual cortex.
What is a critical period?
The period of time in which the networks for each contributing eye (or other sensory modality) is created within the brain.
Why can frequent otitis media infections in infants lead to permanent deafness?
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.
Why will there be no ocular dominance (rather 50/50 distribution) column disruption if both eyes are closed from birth?
Because activity and cortical representation is relative, not absolute.
