Ch 8

• Structural development


  Can be correlated with emerging behaviors
• Behavioral development


  Can predict the underlying circuitry that must be emerging
• Factors that influence brain structure and behavioral development

  • Hormones
  • Injury
  • Socioeconomic status (SES)
• Tower of Hanoi


  Tests planning skills and frontal lobe development
• Childhood SES


  Correlates with cognitive development, language, memory, emotional processing, and income/health in adulthood
• Lower family income associated with decreased cortical surface area in widespread regions on frontal, temporal, and parietal lobes
• Idea of preformation was prevalent up until mid-1800s
• Embryos of different species more closely resemble each other than their parents
• Supports Darwin's view – all vertebrates arose from a common ancestor millions of years ago
• Embryonic nervous system of vertebrates

  • 3 chambered brain: forebrain, midbrain, hindbrain
  • Visible in humans at ~28 days

  
• Gross development of the human nervous system

  1. Neural plate: primitive neural tissue that gives rise to the neural tube

  2. Neural tube: structure in early development from which brain and spinal cord arise
• Day 49 (7 wks): embryo begins to resemble a miniature person

  
• Day 60 (9 wks): sexual differentiation occurs
• Day 100 (14 wks): brain looks distinctly human
• 7 months (28 wks): gyri and sulci begin to form
• 9 months (36 wks): brain looks like an adult brain

  
• Stem cells


  Unspecialized cells that can: 1) Reproduce itself indefinitely 2) Differentiate into more than one type of specialized cells

  
• Stem cell types/terminology


  • Totipotent
  • Pluripotent
  • Multipotent
  • Unipotent

  
• Progenitor cell


  Precursor cell derived from a stem cell that migrates and produces a neuron or glial cell

  
• Neuroblast


  Product of a progenitor cell that gives rise to different types of neurons

  
• Glioblast


  Product of a progenitor cell that gives rise to different types of glial cells

  
• Stages of brain development

  • Cell birth (neurogenesis; gliogenesis)
  • Neural migration
  • Cell differentiation
  • Neural maturation (dendrite and axon growth)
  • Synaptogenesis (formation of synapses)
  • Cell death and synaptic pruning
  • Myelogenesis (formation of myelin)

  
• The human brain requires approximately 10 billion cells to form the cortex that blankets a single hemisphere (neurogenesis and gliogenesis)

  
• This means it must produce about 250,000 neurons per minute at the peak of prenatal brain development
• Teratogens


  Factors that can disrupt normal embryonic development
• Intrinsic signals


  Inherited from mother cell
• Extrinsic signals


  Chemical cues received from cell's surroundings
• Symmetric division


  Cell divides into two identical daughter cells
• Asymmetric division


  Cell divides into two different daughter cells
• Dendritic growth


  To provide surface area for synapses with other cells
• Axonal extension


  To appropriate targets to initiate synapse formation
• Brains of individuals with Autism Spectrum Disorder are characterized by accelerated rates of neuronal maturation
• Brains of individuals with Autism Spectrum Disorder have excessive brain volume in the amygdala, temporal, and frontal lobes
• Cell adhesion molecules (CAMs)

  Manufactured by other cells and attached directly to substrate along which growth cones move
• Tropic molecules


  Secreted and diffusible, form a concentration gradient that either attracts or repels pathfinding axons
• There are 100 000 trillion (1014) synapses in the adult human cerebral cortex
• At the peak of synaptic pruning, up to 100 000 synapses/sec may be lost
• Neural Darwinism


  Hypothesis that processes of cell death and synaptic pruning are, like natural selection in populations, the outcome of competition among neurons for connections and metabolic resources in a neural environment
• Radial glia differentiate into astrocytes once neural migration is complete
• Myelination is a useful rough index of cerebral maturation