Brain Development + Plasticity

• What 3 types of germ cells is an embryonic disk made up of?

  Endoderm, Mesoderm, Ectoderm
• Endoderm turns into?

  Organs
• Mesoderm turns into?

  Muscles and bones
• Ectoderm turns into?

  Nervous system and skin
• When does the human CNS form?

  2 weeks
• What forms the hindbrain, midbrain and forebrain?

  Neural tube that forms around a fluid-filled cavity which sinks under the skin surface
• When does cranial nerves form ?

  7 weeks
• Ectoderm: neural plate > neural grove & neural folds > neural tube
• Top end of neural tube > forebrain, midbrain & hindbrain
• Inner cell mass: ectoderm, mesoderm & endoderm
• •  Cells of the neural tube proliferate and migrate outwards.

  •  During migration, neurons differentiate to take their final form.

  •  The axons of neurons are then myelinated, and synapses are formed.

   
• During proliferation, cells lining ventricles divide and some cells become stem cells and some neurons and glia that migrate to other locations
• What chemicals guide primitive neurons and glia to their destinations during migration?


  Immunoglobins and chemokines
• Synaptogenesis

  Formation of synapses between neurons
• Synaptogenesis is final stage of neural development
• Synaptogenesis occurs throughout life as neurons are constantly forming new connections and discarding old ones
• Stages of growth and development of neurons:

  1. Proliferation
  2. Migration
  3. Differentiation
  4. Synaptogenesis
• In humans, myelin forms first in the spinal cord before forming in the brain (from hind to mid to forebrain --- forebrain is last and this has been related to reduced executive function in adolescence).
• Myelination begins during the prenatal period and continues into adulthood.
• Cell bodies in periphery make up cortical gray matter; myelinated axons form the white matter
• What makes up cortical grey matter?

  Cell bodies in periphery
• What makes up white matter?

  Myelinated axons
• Life span of white blood cells?


  less than 2 weeks
• Red blood cells lifespan?

  less than 4 months
• Skin cell lifespan?


  Less than a year
• Life span of brain cells?

  Person's age
• What are two exceptions to brain cell life span a person's age?

  Hippocampus and olfactory receptors
• What did Sperry find out using frogs?

  Presence of chemical gradients
• How did Sperry discover chemical gradients?

  He severed optic nerve axons will grow back to their original targets in the tectum. He showed that this process was dependent on chemical gradients in the target cells by severing the optic nerve and rotating the eye by 180°
• What guides growing axons?

  Chemo-attractants and repellents
• Who found that muscles determine neuronal survival using neurotrophins and apoptosis?

  Levi-Montalcini
• What is nerve growth factor (NGF) ?

  neurotrophin released by muscles that promotes the survival and growth of axons
• The brain’s system of overproducing neurons and then applying apoptosis enables the exact matching of the number of incoming axons to the number of receiving cells
• When does apoptotic process for neurons stop?


  After birth
• What process is used in neuronal survival after birth?


  Neurotrophins
• Later in life neurotrophins is used for neuronal sculpting
• Symptoms of fetal alcohol syndrome


  Decreased alertness, hyperactivity, facial abnormalities, mental retardation, motor problems, heart defects
• How are the symptoms of FAS caused?

  Cortical thinning: alcohol suppresses the release of glutamate > less excitation > apoptosis
• A rich/stimulating environment increases dendritic branching and the number of synapses in the brain.