Brain Development & Plasticity

• Maturation of the vertebrate brain

  1. Formation of the neural tube around a fluid-filled cavity

  2. Development into hindbrain, midbrain, and forebrain

  3. Formation of central canal and four ventricles

  4. Increase in brain weight from 350 grams at birth to 1,000 grams at one year and 1,200-1,400 grams in adults
• Genes are units of heredity that maintain their structural identity from one generation to another
• Epigenetics deals with changes in gene expression
• Ribonucleic Acid (RNA) is a single-strand chemical
• Types of twins


  • Monozogotic twins (one egg)
  • Dizygotic twins (two eggs)
• Heterozygous Gene refers to having an unmatched pair of genes
• Myelination begins during the prenatal period and continues into adulthood
• Deoxyribonucleic Acid (DNA) is a double-stranded molecule
• Homozygous Gene refers to having the same genes on two copies of a chromosome
• Heritability ranges from zero to one, indicating the genetic contribution to the variation
• Recessive Genes show their effects only in the homozygous condition
• Neurons have a suicide program and will automatically die if they don't receive enough NGF
• Chromosomes are strands of genes
• Enzymes are biological catalysts that regulate chemical reactions in the body
• Dominant Genes show a strong effect in either the homozygous or heterozygous condition
• Growth and Development of Neurons

  1. PROLIFERATION: Production of new cells along the ventricles to become neurons and glia

  2. MIGRATION: Movement of primitive neurons and glia towards their final destination guided by immunoglobulins and chemokines

  3. DIFFERENTIATION: Development of axon and dendrites distinguishing neurons from other cells

  4. MYELINATION: Production of myelin sheaths around axons for rapid transmission

  5. SYNAPTOGENESIS: Formation of synapses throughout life
• Neuronal survival is determined by the release of nerve growth factor (NGF) by muscles, promoting the survival and growth of axons
• Histones bind DNA into a shape more like string wound around a ball
• Brain Derived Neurotrophic Factor (BDNF)


  • Most abundant neurotrophin in the adult mammalian cortex, involved in the loss of excess neurons during development
• Adolescents are impulsive and prone to seek immediate pleasure, but can make mature decisions when given time to consider options
• The developing brain is more vulnerable to malnutrition, toxic chemicals, and infections compared to the mature brain
• Brain damage can result from various causes including tumors, infections, exposure to radiation or toxic substances, and degenerative conditions like Parkinson’s and Alzheimer’s disease
• Prenatal exposure to cocaine or cigarette smoking is associated with attention deficit/hyperactivity disorder (ADHD) and other behavioral deficits
• Axons that don’t receive enough NGF degenerate and their cell bodies die
• Synapses


  Connections between neurons
• All neurons are born with a suicide program and will automatically die if the right synaptic connection is not made
• Fetal Alcohol Syndrome is caused by alcoholic consumption during pregnancy and leads to various developmental issues
• Apoptosis


  A programmed mechanism of cell death
• Memory and reasoning tend to fade beyond age 60 due to slower synaptic alterations and decline in hippocampal volume
• Closed head injuries, caused by sharp blows to the head, are the most common cause of brain damage in young people
• Children exposed to antidepressant drugs during pregnancy have an increased risk of heart problems
• Muscles produce and release nerve growth factor (NGF), which promotes the survival and growth of axons
• Infant brains are sensitive to alcohol as it suppresses the release of glutamate, leading to neuronal apoptosis
• Neurotrophin


  Chemical that promotes the survival and activity of neurons
• Children of impoverished or abused mothers have increased problems in both academic and social functioning
• Nerve Growth Factor (NGF)


  • Promotes the survival and growth of the axon
• Higher performing older adults activate more brain areas to compensate for less efficient activity
• Closed head injuries damage the brain due to rotational forces that drive brain tissue against the inside of the skull
• Diaschisis


  Decreased activity of surviving neurons after other neurons are destroyed. Behavioral deficits due to diaschisis can sometimes be improved with the use of stimulant drugs
• Collateral sprouts


  Newly formed branches from uninjured axons that attach to a synapse vacated when the original axon was destroyed. This process is initiated by neurotrophins secreted by the cells that have lost their source of innervation