Neurofibrillary tangles are one of the two anatomical hallmarks that define Alzheimer’s disease (AD). The other hallmark is amyloid plaques. Technically, an individual may display all the behavioral and cognitive symptoms of AD, but if the brain does not contain the hallmark plaques and tangles, there is no diagnosis of AD.
Normally, every brain cell or neuron contains long fibers made of protein which act as scaffolds, holding the neuron in its proper shape and also helping transport of nutrients within the neuron. In AD, these fibers begin to twist and tangle. The neuron loses its shape and also becomes unable to transport nutrients properly; it eventually dies. The fiber tangles remain in the brain long after the dead neuron has been cleared away.
by Catherine E. Myers. Copyright © 2006 Memory Loss and the Brain