Brian

• Brain


  • Plastic
  • Living organ
  • Changes all the time due to response to its genetic program and environment
• Neurodevelopment


  1. Begins with a single fertilized egg cell

  2. Ends with a functional adult brain

  3. Five phases: neural plate induction, neural proliferation, migration and aggregation, axon growth and synapses formation, neuron death and synapse rearrangement
• Neural plate


  A small patch of ectodermal tissue on the dorsal surface of the developing embryo, destined to develop into the human nervous system
• Stem cells


  Cells of the neural plate that have an almost unlimited capacity for self-renewal and the ability to develop into many different kinds of cells
• Neural tube development


  1. Develops into the cerebral ventricles and spinal cord

  2. Forebrain, midbrain, and hindbrain develop from 3 swellings
• Neural proliferation


  Cells in the neural tube begin to proliferate, with most cell division occurring in the ventricular zone
• Migration


  1. Radial migration - cells move outward from the ventricular zone

  2. Tangential migration - cells move parallel to the tube walls

  3. Somal translocation and glia-mediated migration
• Aggregation


  Migrating neurons align themselves with other developing neurons to form nervous system structures, mediated by cell-adhesion molecules and gap junctions
• Axon growth


  Growing axons and dendrites are guided by attractive and repulsive signals, with pioneer growth cones leading the way
• Synapse formation


  Axons establish synapses with appropriate target neurons, with glial cells and chemical signals playing a role
• Neuron death


  Active apoptosis and passive necrosis of neurons, triggered by genetic programs and failure to obtain survival factors
• Nerve growth factor (NGF) and neurotrophins

  Chemicals that promote growth, survival, and synaptogenesis of neurons
• Postnatal brain growth


  • Synaptogenesis, myelination of axons, increased branching of dendrites
• Myelination of sensory areas occurs in the first few months after birth, followed by motor areas, with the prefrontal cortex continuing into adulthood
• Cortical thinning


  Periods of synaptic and gray matter loss that occur at different times in different parts of the brain, with sensory and motor areas reaching functional maturity before association areas
• Development of the prefrontal cortex

  • Responsible for working memory, planning, inhibition, and social behavior
  • Prefrontal development is prolonged compared to other brain regions
• Perseveration


  Tendency to continue making a formerly correct response when it is currently incorrect, due to immature prefrontal cortex
• Permissive experiences


  Experiences that permit the expression and maintenance of genetic programs of brain development
• Instructive experiences


  Experiences that contribute to and influence the course of brain development
• Critical periods


  Intervals during which specific experiences must occur to influence development
• Sensitive periods


  Intervals during which experiences have a greater effect on development, but can still have weaker effects outside
• Sensory deprivation and environmental enrichment have been shown to affect the development of the visual cortex and other brain regions
• Neuroplasticity in adults


  The brain can undergo substantial reorganization and change in adulthood, including the growth of new neurons (neurogenesis)
• Adult neurogenesis


  Occurs in the striatum, hippocampus, and olfactory bulb, with new neurons becoming integrated into neural circuits
• Pattern separation


  The ability to separate distinct percepts into individual memories for storage, which is facilitated by adult hippocampal neurogenesis
• Experience in adulthood can lead to reorganization of sensory and motor cortical maps, and the brain can adapt more effectively to repeated exposure to abnormal environmental conditions