Neurodevelopment

Question 1

Neurulation

Answer 1

The formation of the neural tube - starts about 22 days after conception

Question 2

Neural plate

Answer 2

• Key developmental structure that serves as the basis for the nervous system → appears around 17 days after conception
• Thickened plate of ectoderm along the dorsal midline of the early vertebrate embryo
• Gives rise to the neural tube and neural crests.

Question 3

Ectoderm

Answer 3

The outermost layer of cells or tissue of an embryo in early development

Question 4

Notochord

Answer 4

A cylinder-like strucutre in the mesoderm. Progenitor of the spine.

Question 5

Neural crest

Answer 5

• A group of ectodermal cells that develop into tissue of the spinal and autonomic ganglia and connective tissue around the CNS → PNS.
• Occurs around 22 days after conception.

Question 6

Neural tube

Answer 6

• A tube formed by the closure of ectodermal tissue (neural plate) in the early embryonic development that later develops into the brain, spinal cord, nerves and ganglia → CNS
• Occurs around 22 days after conception

Question 7

Somites

Answer 7

Thickening of mesodermic cells which give rise to skeletal muscles etc.

Question 8

Gastrulation

Answer 8

Phase of embryonic development by which the embryo begins to take its multicellular from in a process called invagination in which the infolding of embryonic cells produces 3 layers:

• ectoderm (outer layer)
• mesoderm (middle layer)
• endoderm (inner layer)

Question 9

Spina bifida

Answer 9

• Neural tube defect where there is a failure of the lower neural spinal tube to close
• Spine exposed to intrauterine environment
• Can have bladder/bowel problems or weakness in legs
• Individuals affected may suffer from motor and sensory defects in the legs, incontinence, vertebral curvature and increased CSF pressure in the brain

Question 10

Anencephaly

Answer 10

• Failure of upper neural tube to close
• Results in a baby being born without the front part of the brain (forebrain) and the thinking and coordinating part of the brain (cerebrum).
• Often infants do not survive longer than a few hours after birth
• Oftern blind, deaf and unable to feel pain

Question 11

Stages of brain development

Answer 11

1. Neurulation: induction of the neural plate
2. Proliferation: production of new cells
3. Migration: movement of newly formed neurons to their eventual locations
4. Differentiation: forming of axons and dendrites
5. Myelination: glia produce fatty sheath that covers axons
6. Synaptogenesis: formation of synapses between neurons

Question 12

Neural proliferation

Answer 12

• Phase in brain development in which new cells are generated
• Cells lining in the ventricles divide, some of which become stem cells (omnipotent; can develop to any cell in the body; can divide)
• Others become neuroblasts or precursor cells (can become any cells of the nervous system; can divide)
  
  • neurons
  • glial cells

Question 13

Cell migration

Answer 13

• Process in which cells of the brain arrive at their specific location
• Process is facilitated by radial glia, a network of guidewires and support structures that the migrating neuron wraps around and follows to its destination
• Human neo-cortex has got 6 layers each formed of slightly different cells → During development of NS these layers are set up one after the other (with the lower layers to be the first i.e. layer VI, V, IV, III, II, I respectively)
  • Failure to proper migration can lead to malorganisation of cortical layers causing developmental dyslexia

Question 14

Cortical layers

Answer 14

6 layers differentiated by cell types and function:

• Layer 1: outer layer. Few cell bodies, mainly axons and dendrites.
  
  • Receives non-specific afferents.
• Layer 2: contains granule cells (cells with small bodies).
  
  • Receives signals from cortical afferents
• Layer 3: contains pyramidal cells (large cell bodies)
  
  • Contains interhemispheric and cortical association fibres
• Layer 4: contains granule cells (cells with small bodies)
  
  • Receives signals from thalamic afferents
• Layer 5: contains pyramidal cells (large cell bodies)
  
  • Contains efferent projections to the neostriatum, brainstem and spinal cord
• Layer 6: contains pyramidal cells and spindle-shaped cells
  
  • Neurons project to the thalamus

Question 15

Myelination

Answer 15

Developmental phase whereby glia cells provide myelin around some neurons that increases the speed of neurotransmission

Question 16

Arborisation

Answer 16

Developmental phase whereby differentiated neurons grow dendrites and form connections

Question 17

Synaptogenesis

Answer 17

• Final developmental stage whereby neurons form synapses to communicate amongst one another.
• This process is ongoing throughout life.
• Synapses are dependent upon experiences and interactions with an environment - it is at the synapse where learnig takes place

Question 18

Pruning

Answer 18

• Process which addresses the overproduction of synapses: synapses that are used a lot become stronger and those not used are pruned away
• Lack of pruning causes very high brain volume and disorganised structure → autism

Question 19

Apoptosis

Answer 19

• Process by which neurons die after cellular migration.
• This happens because cells fail to compete for neurotrophins (chemicals that promote growth and survival of neurons and stimulate synaptogenesis) at their target site.
• Synaptogenesis is assisted by nerve growth factor (NGF), which is a protein that promotes the survival of only certain neurons → neural Darwinism