Alzheimer's disease brain cell. Coloured transmission electron micrograph (TEM) of a neurofibrillary tangle in a nerve cell from the brain of a patient with Alzheimer's disease. The tangle (pink) lies in the cytoplasm (orange) of the cell, and consists of abnormal aggregates of the protein tau. In the healthy cell, tau stabilises microtubules in the cytoplasm. It is not known precisely how the tangles are formed, nor their impact on the neuron's function, but they are seen in a range of neural disorders including Alzheimer's disease, Creutzfeld-Jakob disease (CJD), some forms of Parkinson's disease, and Supranuclear Palsy.