What is Alzheimer’s disease? How does it affect the brain?

alzheimer's disease

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A type of dementia. It causes problems in memory, thinking and behavior. In general, Alzheimer’s disease is associated with memory loss and cognitive abilities.

  • (60 – 70)% of dementia cases in the world are Alzheimer’s cases.
  • It usually affects adults (65 years or older), and it may affect younger people.
  • Nearly 200,000 Americans under the age of 65 have been diagnosed with this disease.
  • Alzheimer’s is the sixth leading cause of death in the United States.

Symptoms of Alzheimer’s disease

It appears gradually on the person with a slow progression that begins with a slight loss of memory to the individual’s inability to engage in a conversation or respond to the surrounding environment, or even perform daily functions. The more time passes, the symptoms appear worse than before.

alzheimer's disease
alzheimer’s disease

People with the Alzheimer’s disease show certain signs:

  1. Difficulty in remembering newly acquired information (because it starts in the learning part of the brain).
  2. Confusion about events, time, and location.
  3. Changes in mood and behavior.
  4. Doubts about family, friends, and caregivers.
  5. Loss of important memories and change in behavior.
  6. Difficulty talking, swallowing and walking.

Most affected people do not realize that they have a problem. Signs appear clearly more to family and friends.

What happens to the brain in Alzheimer’s disease?

Microscopic changes in the brain begin long before the first sign appears.

In the brain, there are nearly 100 billion nerve cells (neurons), each neuron communicating with another group of neurons that make up communication networks.

nerve cells network
nerve cells network

Neurons are functionally divided into several groups, each group responsible for a specific function, such as learning, thinking, remembering, seeing, smelling, listening, taste..etc.

These groups work in harmony with each other in an integrated way so that the brain performs all its functions in a perfect way. It is like a small factory where cells receive supplies, generate power, produce and gets rid of waste. It also organize the consumption of fuel and oxygen among them.

The cells process the information, store it, and then communicate with another group of cells to ensure the continuity of the brain’s functions.

Alzheimer’s disease begins with problems in the work of some cells, which affects the work of other cells, and it continues to expand until it includes the performance of the brain as a whole.

The reasons of  having Alzheimer’s disease

Toxic changes happen in the brain, which affect its balance. These changes include the wrong formation of some proteins that play an important role in causing disease and affecting cell functions. As tau protein, and Beta-amyloid protein.

tau and beta-amyloid proteins
tau and beta-amyloid proteins

The tau protein accumulates abnormally inside neurons, forming tangles.

Beta-amyloid accumulates into plaques, which are slowly building up in the space between neurons.

As the amyloid reaches a tipping point, the tau protein is rapidly spread throughout the brain.

tangles and plaques
tangles and plaques

There are other changes in the brain that may play an important role in causing Alzheimer’s disease, as the vascular system may fail to deliver enough oxygen and nutrients to the brain. This causes a lack in the glucose, that is needed to supply cells with energy.

Infection of glial cells may disrupts its function to get rid of waste. Infection of glial cells also affects the response of astrocytes.

Eventually, the neurons lose their ability to communicate, and they die. Which leads to a shrinkage of the brain starting with the hippocampus (the part responsible for learning and the memory), which causes the experience of memory loss, inability to make decisions, language problems, and inability to perform daily functions.

brain shrinkage in alzheimer's disease
brain shrinkage in alzheimer’s disease

Alzheimer’s at the DNA level

Having a parent with Alzheimer’s doesn’t mean that offspring will definitely get it, but this makes them more likely to have it.

If a mutant gene is inherited, this may increase the risk of developing it in early or late stages of life.

Genetic variables may increase or decrease the risk of disease, this occurs when the proportion of a genetic variable increases without directly causing disease, as this condition is called the genetic risk factor. Knowing these factors may help find a way to deal with them.


No specific gene has been found to be directly responsible for Alzheimer’s disease, but genes related to the appearance of the disease have been identified as the genetic variables of the apolipoprotein E (APOE) gene in chromosome 19. The APOE gene contributes to the production of auxiliary protean that carries cholesterol and other types of fats in the bloodstream .

Treatment of Alzheimer’s

No cure has been found for the disease. Treatment includes dealing with symptoms such as trying to slow disease progression and improving the quality of life for patients and their families, but it cannot stop the disease,

Scientists try to understand the disease at molecular levels
Scientists try to understand the disease at molecular levels

Scientists try to understand the cellular and molecular pathways and how they interact, trying to develop an effective treatment against the disease.

The technological development of scanning the brain and pathways inside of it also contributes to build an understanding of the formation of toxic accumulates of proteins in the living brain. Researchers are studying the vascular system and genetic factors trying to follow all related changes. Also they are studying the role of exercises, healthy diets and psychological factors have to protect against Alzheimer’s disease.[1]https://www.alz.org/alzheimers-dementia/what-is-alzheimers [2]https://www.nia.nih.gov/health/alzheimers-disease-genetics-fact-sheet [3]https://www.nia.nih.gov/health/what-happens-brain-alzheimers-disease

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