Neurofibrillary tangles are abnormal clumps of protein that form inside nerve cells, primarily composed of a protein called tau. These tangles disrupt the normal functioning of neurons, leading to cell damage and death. They are commonly associated with neurodegenerative diseases, particularly Alzheimer's disease. The presence of neurofibrillary tangles is often used as a key indicator in diagnosing Alzheimer's disease and other forms of dementia. As the disease progresses, the accumulation of these tangles correlates with cognitive decline and memory loss, highlighting their significance in understanding and studying neurodegenerative disorders.