The brain has 100 billion nerve cells (neurons). Each nerve cell connects with many others to form communication networks.

Groups of nerve cells have special jobs. Some are involved in thinking, learning and remembering. Others help us see, hear and smell. Still others tell our muscles when to move. Nerve cells are the chief type of cell destroyed by Alzheimer's disease.

Scientists believe that whatever triggers Alzheimer’s begins to damage the brain years before symptoms appear. When symptoms emerge, nerve cells that process, store and retrieve information have already begun to die. The death of nerve cells is what causes memory failure, personality changes, problems in carrying out daily activities and other symptoms of Alzheimer’s disease.

The role of plaques and tangles

The brains of individuals with Alzheimer’s have an abundance of plaques and tangles. Scientists believe plaques and tangles play a critical role in blocking communication among nerve cells and disrupting processes the cells need to survive.

• Plaques build up between nerve cells. They contain deposits of a protein fragment called beta-amyloid (BAY-tuh AM-uh-loyd).

• Tangles are twisted fibers of another protein called tau (rhymes with “wow”) that form inside brain cells.

In a person with Alzheimer’s, plaques and tangles tend to develop in a predictable pattern, beginning in the areas important for memory before spreading to other regions.

Inside the Brain: An Interactive Tour Learn how the brain works and how Alzheimer's affects it.

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