PHYP211 Week 5

• The human central nervous system begins to form when the embryo is about two weeks old, with a neural tube forming around a fluid-filled cavity that eventually develops into the hindbrain, midbrain, and forebrain
• The fluid-filled cavity becomes the central canal and the four ventricles in the brain
• At birth, the human brain weighs approximately 350 grams, increasing to around 1,000 grams at one year of age, and the average adult brain weighs between 1,200 and 1,400 grams
• The five steps of neuron development:

  • Proliferation: Production of new cells, cells along the ventricles of the brain divide to become neurons and glia.
  • Migration: Movement of primitive neurons and glia toward their final destination in the brainns and glia toward their final destination in the brain
  • Differentiation: Neurons develop axons and dendrites
  • Myelination: Glia cells produce myelin sheaths around axons for rapid transmission
  • Synaptogenesis: Formation of synapses
• Rita Levi-Montalcini discovered that muscles producing and releasing nerve growth factor (NGF) promote the survival and growth of axons, determining which synapses survive
• All neurons are born with a programmed cell death called apoptosis, where neurons automatically die if the right synaptic connection is not made
• Neurotrophins like NGF and brain-derived neurotrophic factor (BDNF) promote the survival and activity of neurons
• The developing brain is more vulnerable to malnutrition, toxic chemicals, and infections compared to the mature brain
• Fetal Alcohol Syndrome is caused by alcohol consumption during pregnancy and can lead to symptoms like decreased alertness, hyperactivity, facial abnormalities, mental retardation, and motor problems
• Prenatal exposure to substances like cocaine, cigarette smoking, or antidepressant drugs can have negative effects on brain development
• Adolescents are impulsive and prone to seek immediate pleasure, but research shows they can make mature decisions when given time to consider options carefully
• Brain damage can result from various causes, including tumors, infections, exposure to toxic substances, and degenerative conditions like Parkinson’s and Alzheimer’s disease
• Closed head injuries, caused by a sharp blow to the head, are the most common cause of brain damage in young people
• Diaschisis is a decreased activity of surviving neurons after other neurons are destroyed, and stimulant drugs can sometimes improve behavioral deficits due to diaschisis
• Under certain circumstances, damaged axons can regrow, but regeneration is minimal in the mature mammalian central nervous system
• Axon sprouting is a normal process where the brain constantly adds new branches of axons and dendrites, accelerating in response to damage
• Collateral sprouts are newly formed branches from uninjured axons that attach to synapses vacated when the original axon was destroyed