Alzheimer's disease brain tissue. Light micrograph of entorhinal cortex brain tissue affected by Alzheimer's disease. Two characteristic features are seen here: neurofibrillary tangles (brown) and neuritic plaques (grey). Neurofibrillary tangles are formed of abnormal filaments of tau protein, an internal structural component of healthy nerve cells. The pathogenic abnormal form has no struct- ural role, and damages the cells. The neuritic plaques are formed mainly of aggregations of the protein amyloid. Alzheimer's disease causes progr- essive impairment of mental function, leading to memory loss, dementia and death. Stained with anti-tau serum. Magnification: x50 at 35mm size.