What are amyloid plaques and neurofibrillary tangles as related to Alzheimer’s disease?

The accumulation of amyloid plaques found between nerve cells (neurons) in the brain is one of the characteristic traits of Alzheimer’s disease. The other hallmarks of the disease are the insoluble twisted fibers found inside the brain cells, which are called neurofibrillary tangles. The amyloid plaques and neurofibrillary tangles are buildups of protein, which also occur as part of our normal aging process. In Alzheimer’s, however, these buildups of proteins are much greater.

Also known as senile plaques, amyloid plaques consist of small, dense deposits of a specific protein called beta-amyloid, which develop from a larger protein present in the membrane surrounding healthy nerve cells. The beta-amyloid molecules are chemically adhesive and gradually stick to one another to form the plaques.

For the most part, plaques are located in the hippocampus, the part of the brain where memories are encoded, and also in other regions of the cerebral cortex that are important for thinking and making decisions. As Alzheimer’s disease progresses in the individual, the number of plaques increase and their distribution in the brain spreads.

Neurofibrillary tangles consist primarily of a protein called tau that forms part of a cell structure called a microtubule. This microtubule assists in transporting nutrients and other substances from one part of the nerve cell to another. In Alzheimer’s disease, the tau protein is abnormal and the microtubule structures collapse; hence, they separate into filaments that form the tangles, and damage the ability of neurons to communicate with each other.

Neurons are cells within the nervous system that transmit information to other nerve cells, muscle or gland cells. The brain is made up of 100 billion neurons that send messages throughout the body. The operation and function of the brain are conducted by these neurons. Neurons can communicate with another 10,000 neurons, however, one neuron never touches another neuron, but the two cells communicate chemically and this union is called a synapse.

In Alzheimer’s disease, the plaques and tangles damage synapses, and there is a gradual loss of connection (communication) between neurons, which eventually causes cell death. As the neurons die throughout the brain, the affected regions begin to shrink (brain atrophy).

In the final stage of Alzheimer’s disease, damage is widespread and brain tissue has shrunk significantly.

Questions about Alzheimer’s disease or a related dementia disorder? Contact Dana Territo, the Memory Whisperer, Director of Services at Alzheimer’s Services of the Capital Area, (225) 334-7494, advice@alzbr.org, or visit the organization at 3772 North Blvd., Baton Rouge.