Why does Alzheimer's Disease Occur



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Chapter 2 : Why does Alzheimer's disease Occur?



The Role of Plaques and Tangles arrow_upward


  • Scientists can also see the terrible effects of Alzheimer's disease when they look at brain tissue under the microscope.
  • Alzheimer's tissue has many fewer nerve cells and synapses than a healthy brain.
  • Plaques, abnormal clusters of protein fragments, build up between nerve cells.
  • Dead and dying nerve cells contain tangles, which are made up of twisted strands of another protein.
  • Scientists are not absolutely sure what causes cell death and tissue loss in the Alzheimer's brain, but plaques and tangles are prime suspects.

  • More about Plaques arrow_upward


  • Plaques form when protein pieces called beta-amyloid clump together.
  • Beta-amyloid comes from a larger protein found in the fatty membrane surrounding nerve cells.
  • Beta-amyloid is chemically "sticky" and gradually builds up into plaques.
  • The most damaging form of beta-amyloid may be groups of a few pieces rather than the plaques themselves.
  • The small clumps may block cell-to-cell signaling at synapses.
  • They may also activate immune system cells that trigger inflammation and devour disabled cells.

  • More about Tangles arrow_upward


  • Tangles destroy a vital cell transport system made of proteins.
  • This electron microscope picture shows a cell with some healthy areas and other areas where tangles are forming.

  • In healthy areas:

  • The transport system is organized in orderly parallel strands somewhat like railroad tracks.
  • Food molecules, cell parts and other key materials travel along the "tracks."
  • A protein called tau helps the tracks stay straight.

  • In areas where tangles are forming:

  • Tau collapses into twisted strands called tangles.
  • The tracks can no longer stay straight. They fall apart and disintegrate.
  • Nutrients and other essential supplies can no longer move through the cells, which eventually die.

  • Progression through the Brain arrow_upward


  • Plaques and tangles (shown in the blue-shaded areas) tend to spread through the cortex in a predictable pattern as Alzheimer's disease progresses.
  • The rate of progression varies greatly. People with Alzheimer's live an average of eight years, but some people may survive up to 20 years.
  • The course of the disease depends in part on age at diagnosis and whether a person has other health conditions.
  • Earliest Alzheimer's - changes may begin 20 years or more before diagnosis.
  • Mild to moderate Alzheimer's stages - generally last from 2 - 10 years.
  • Severe Alzheimer's - may last from 1 - 5 years.


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