Plaques and Tangles
Amyloid Plaques and Tau Tangles are believed to be the two molecules responsible for the brain damage associated with Alzheimer's disease. Both Plaques and Tangles are present in the brains of individuals without Alzheimer's; however, they are found at much higher levels in the brains of Alzheimer's patients.
It is theorized that the root causes of Alzheimer's disease are the factors which control the amount of Amyloid and Tau in the brain. Factors like the ApoE gene.
Amyloid Plaques Damage Brain Cells
Amyloid is a naturally occurring protein in the human body and brain. During Alzheimer's, normal Amyloid groups suffer from a structural change which disrupts normal functioning.
One abnormal amyloid group causes other healthy amyloid groups near it to also mutate, eventually they form large groups of amyloid deposits, called plaques or fibrils.
These plaques damage brain cells and cause the brain lesions characteristic of Alzheimer's disease. These plaques can be seen in the image above as the brown cloud-like substance damaging the neuron cells.
Tau Tangles Prevent Brain Cells From Communicating
Tau is another naturally occurring protein in the human body and brain. Its primary purpose in the brain is to stabilize the axons of brain cells. The axon is the part of the cell through which electrical signals travel.
In Alzheimer's disease, tau proteins suffer from a structural change which causes them to pair with other threads of tau. The tau, now tangled with other tau, is no longer able to stabilize the brain cell's axon; the axon subsequently unravels and ceases to exist.