Scientists have identified several hallmark Alzheimer's brain abnormalities:
- Plaques, microscopic clumps of a protein called beta-amyloid peptide. Plaques, abnormal clusters of protein fragments, build up between nerve cells. Alzheimer tissue has many fewer nerve cells and synapses than a healthy brain.
- Dead and dying nerve cells contain tangles, which are made up of twisted strands of another protein called tau (rhymes with "wow")
- Plaques and tangles tend to spread through the cortex in a predictable pattern as Alzheimer's disease progresses.
- Loss of connections among brain cells responsible for memory, learning and communication. These connections, or synapses, transmit information from cell to cell.
- Inflammation resulting from the brain's effort to fend off the lethal effects of the other changes under way
- Eventual death of brain cells and severe tissue shrinkage
Scientists are not absolutely sure what causes cell death and tissue loss in the Alzheimer brain, but plaques and tangles are prime suspects.
In the Alzheimer's brain:
- The cortex shrivels up, damaging areas involved in thinking, planning and remembering.
- Shrinkage is especially severe in the hippocampus, an area of the cortex that plays a key role in formation of new memories.
- Ventricles (fluid-filled spaces within the brain) grow larger.
All these processes have a devastating impact on the brain, and over time, the brain shrinks dramatically, affecting nearly all its functions. Alzheimer's disease leads to nerve cell death and tissue loss throughout the brain. Over time, the brain shrinks dramatically, affecting nearly all its functions.
The rate of progression of the disease 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.
The Stages of Alzheimer's: A Timeframe
- 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.