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

• Anecephaly::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)