neurodevelopment

• embryo

  three layers each with diff cells in them

  • endoderm
  • mesoderm
  • ectoderm

  
• Neurulation

  formation of neural plates

  formation of neural folds and groove

  Tips of neural folds fuse together to form neural tubes

  
• closure of neural tube

  closure of neural tube on day 22

  close starts at neck then spreads in both directions for full closure

  
• formation of brain 1

  anteria part of neural tube forms vesicles

  swells into three vesicles - forebrain midbrain and hindbrain

  forebrain vesicles further differentiate:

  • telencephalic vesicles - cerebral hemispheres
  • diencephalon = thalamus and hypothalamus
  • optic vesicles optic nerve and retina

  
• formation of brain 2

  differentiation of telencephalon

  
• neural crest cells

  cells at tips of neural tubes

  • neurones with cell bodies outside brain and spinal cord (PNS)
  • neurones in gut
  • pigment cells of skin
  • parts of skull
• Developmental defects - SPINA BIFIDA

  if neurone tube doesn't close in spinal region - most common in lower back - paralysis below this region
• Developmental defects - ANENCEPHALY

  neural tube in brain region fails to fuse
• Developmental defects - HIRSCHSPRUNGS DISEASE

  failure of neural crest cells to migrate to large intestine (colon)

  No autonomic nervous system innervation of the large intestine

  No peristalsis

  Constipation
• Neurogenesis

  LUMEN - form brain ventricles

  cells come from sub ventricular zone - region adjacent to the lumen of neural tube

  • contains neural stem cells = neuroepithelial cells
  • produces neurones and glial cells

  
• neuronal fate specification

  exposure to protein concentration gradient

  • bone morphogenic protein (BMP)
  • sonic hedgehog (SHH) protein
• Reduced cell proliferation caused by environmental insults

  Toxins e.g. sodium valproate

  Infectious agents e.g. Rubella

  Undernutrition

  Maternal inflammation

  Neurodevelopmental disorders e.g. autism, schizophrenia
• cell migration

  radial glial cell divides

  symmetrical division

  • 1 radial glial cell = 2 radial glial cell

  asymmetrical division

  • 1 radial glia cell = 1 radial glial cell and 1 neurone
• cortex formation

  divided into layers with different neurones

  
• how to make a connection

  • neurones send out processors - neurites
  • growth cone at the tip of neurite navigate the process towards its target extending the neurite along the way
  • moves towards target via protein - protein interactions
  • Growth cone expresses range of receptors to detect guidance cubes – different in each cone
• Cell death

  competition for trophic factors

  • nerve growth factor (NGF)
  • Brain Derived Neurotrophic Factor (BDNF)
  • Trophic factors released from postsynaptic neurone bind to receptors on presynaptic neurone
  • Trophic factors inhibit programmed cell death (apoptosis)
• After birth

  • production of glial cells - maximal in first 2 years
  • formation of synapses - peaks at 2 years
  • myelination - contimues into 20s and 30s