Alzheimer's disease is a slow and progressive destruction of neurons in the brain. The damage affects specific parts and can be deep within the structure as well as in the outer areas. The defining characteristic of Alzheimer's disease is the appearance of two different structures in the brain tissue called amyloid plaques and neurofibrillary  tangles. The plaques are made up of a normally harmless protein called beta-amyloid.

It's believed that deposits of plaque form between neurons early on in the disease process, before neurons begin to die and symptons develop. Although the ultimate case of neuron death in Alzheimer's isn't known, many researchers believe that an abnormal form of beta-amyloid protein may be the culprit.

The internal support structure for brain neurons depends on the normal functioning of a protein called tau. In people with Alzheimer's, threads of tau protein undergo alterations that cause them to become twisted to form neurofibrillary tangles. It seems likely that the development of tangles within neurons may seriously damage them and cause them to die.