What Does Alzheimer’s Do to the Brain?

Reviewed by: HU Medical Review Board | Last reviewed: January 2023

Cells in the brain, called neurons, carry information. Connections between neurons are what allow different parts of the brain to talk to each other – and the rest of the body. These connections, and the health of neurons, are necessary for brain function including thinking and memory.1,2

But if you have Alzheimer’s disease, these connections do not work as well. Things you may have remembered easily before Alzheimer’s become difficult or impossible to remember. This is a result of Alzheimer’s impacting your brain and its neurons.1,2

How does Alzheimer’s affect the brain?

Normally as you age, the brain shrinks to some degree. This is because the brain does not make many new neurons as you age. Neurons that are not working properly get cleared away, leaving fewer than before. But you do not lose a large number.1

Alzheimer’s disease destroys neurons and their connections. It mostly targets neurons in the areas of the brain that are involved in memory, called the hippocampus and entorhinal cortex. This is what causes the earliest symptoms, such as confusion and difficulty remembering things.1,2

As Alzheimer’s progresses, other areas of the brain are affected, too. As these areas become damaged, it becomes more and more difficult for them to carry out their usual processes. The areas that become damaged include those responsible for:1,2

  • Reasoning
  • Language
  • Social behavior

Alzheimer’s affects neurons in the brain in different ways. Microglia – the cells responsible for clearing away waste and proteins in the brain – do not work as well. This leads to inflammation and accumulation of a harmful protein called beta-amyloid.1

Alzheimer’s also affects the vascular (blood) system in the brain. For people without Alzheimer’s, nutrients are distributed through the brain across the blood-brain barrier while harmful agents are cleared away. But for people with Alzheimer’s, this barrier does not work as well. Without the blood-brain barrier functioning correctly, the brain cannot get rid of toxic beta-amyloid plaques and tau proteins.1

What are beta-amyloid plaques, tau protein, and neurofibrillary tangles?

Beta-amyloid plaques and neurofibrillary tangles are the hallmarks of Alzheimer’s disease. Each of these affects neurons and how they communicate with each other.2

Tangles are bundles of a protein called tau that accumulate within neurons and block communication. When neurons are healthy, they have an internal support structure called microtubules. Tau protein normally helps these microtubules support the cell.1

But in people with Alzheimer’s, tau proteins stick to each other. They create tangles within the neurons, called “neurofibrillary tangles.” Tangles block the neurons from working the way they are supposed to. This makes communication between neurons much harder.1

Plaques are deposits of harmful protein called beta-amyloid and waste from cells that build up outside and around neurons. Together, plaques and tangles are what damage neurons and their connections in the brains of people with Alzheimer’s.1,2

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