Animation showing the pathology of Alzheimer's disease. Initially the view zooms in to a healthy brain, showing the millions of neurons sending and receiving signals. It then focuses on one synapse, where a nerve cell axon passes a chemical signal to the body of another nerve cell. The axon opens to show its interior, consisting of synaptic vesicles (pink) containing neurotransmitters moving up and down microtubules. Each microtubule is made up of the protein tubulin (blue), which is stabilised by another protein called tau (brown). In Alzheimer's disease the tau breaks down, damaging the microtubule and leading to the formation of disruptive tangles of abnormal tau protein. Outside the nerve cells, a common protein called amyloid precursor protein is broken up into smaller chunks of beta-amyloid (purple). These clump together in senile plaques, which also impair nerve function. The plaques and tangles are characteristic of Alzheimer's disease. The death of nerve cells leads to marked atrophy in the brain, as seen in the comparison at the end.