Neuron in Alzheimer's disease, transmission electron micrograph (TEM). Within the neuron (nerve cell) are abnormal aggregates and insoluble fibres of the protein tau, known as 'paired helical filament' (PHFs, stack of thin parallel lines). Tau protein is an abundant neural protein, aggregations of which are thought to play a role in Alzheimer's disease and other neural disorders. Lipofuscin (dark spheres, centre right) are pigment granules that may contribute to the formation of amyloid plaques and the death of neurons. Magnification: x3,600 when printed at 10 centimetres wide.