Development of the Brain (Chapter 4)

The Beginning of Development:

• Fertilization of an egg - immediate change to the cells, they begin dividing - the tissue divides itself into 3 layers
  • ==Ectoderm==::skin, nervous system
  • ==Mesoderm==::muscles and bones
  • ==Endoderm==::GI and res tracts, endothelial cells
• Neural plate will form - ==neural crest== will fuse and set up foundation for the brain and spinal cord
  • Forms central canal and becomes the ==neural tube== - goes all the way thru entire length of cells (brain is at the anterior)
  • Divides out into the forebrain, midbrain, hindbrain (brain stem), and dorsal root ganglion
  • ==Dorsal root ganglion:==:nerves that interface b/w body and spinal cord
  • ==Forebrain:==:cortical regions, thalamus, hypothalamus
  • ==Hindbrain==::cerebellum, pons, medulla

Neural Tube:

• Can cause extreme birth defects if not developed properly
• ==Anecephal==y::does not fuse fully/completely in the anterior, can’t have development of bone, muscle, skin in the brain
  • 100% fatal, 83% die utero or are aborted; 1 in 4,600 in US
  • Causes: folic acid (main cause), genetics (mutations), environment
• ==Spina Bifida==::gap in the fusing of the vertebral column
• ==Meningocele==::dura mater inflates and pops out, grows as the brain produces more spinal fluid
• ==Myelomeningocele==::most severe; posterior region of neural tube, spinal cord fails to fully develop (like anecephaly); causes nerve damage and paralysis
  • ==MOMS study (2003)==::prenatal surgical closure of myelomeningocele

Hydrocephalus:

• Common in Spina Bifida
• Cerebral spinal fluid (which is only made in the outer boundaries of the ventricles) causes compression somewhere along the chamber - sensors further down tell the ventricles to produce more spinal fluid, but the fluid is blocked → keeps making more and more and starts to crush neural tissue
• Can treat by putting a shunt into the lateral ventricle - cerebral spinal fluid will drain thru the tube into the small intestine (almost always naturally rectifies)
• Almost always cognitive deficit if no/late treatment

Stages of Neural Development:

1. ==Cell Proliferation/Neurogenesis==

   1. Once the cells of the neural tube are formed, new cells are produced (neurons); most neocortical neurons are born b/w the 5th week and 5th month of gestation, est. of 250,000/min; occurs nearest to the ventricular zone (VZ)

2. ==Cell Migration==

   1. When glial cells (radial) are made and get a genetic signal that tells them to make long rows → neurons hop on and inchworm up to get where they need to go and then hop off to make their own rows

      1. ==Tangential migration==::parallel to the neural tube
      2. ==Somal translocation==::neuron extends a little sticky arm and zooms to catch up with it

3. ==Cell Differentiation==

   1. Multi-step process determining which cells will be neurons/bones/etc

      1. ==Neuron differentiation==::if the cell is a neuron, what kind of neuron?
      2. Human pluripotent stem cell research

4. ==Synaptogenesis==

   1. Birth of synapses - neurons able to talk to other neurons; distinct processes for different areas of the brain; synaptic pruning after a process of fast development (think of farm to market roads example)

5. ==Cell Death (apoptosis)==

   1. Active cell death - healthy process cleaning up messes/unused pathways; cell death is based on competition; impaired in cancer and neurodegenerative diseases

6. ==Synapse Rearrangement==

   1. Body makes too many synapses to start with so they start to the fine tune their processes and rearrange; growth and complexity increase over time - essential fora health brain

Aging:

• Abilities change across the lifespan - slower reaction time, larger vocab
• Notion of age 65 as “old” doesn’t reflect variability
• Peak performance = 27-30, upkeep of muscle mass after is much harder due to changes in hormone levels
• Balance b/w the body and the brain - both must work together to remain healthy

Cognitive Decline:

• ==MCI==::Mild Cognitive Impairment - prospective memory impairment and weak coding of new info
  • Can maintain MCI or transition into AD
• ==Alzheimer’s==::transition into total memory failure; buildup of beta-amyloid plaques (extracellular) and tau protein tangles (intracellular)

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