Amyloid protein in Alzheimer's disease. Illustration of the processes leading to the formation of amyloid plaques (tangled bundles) on neurons (nerve cells, blue). Amyloid plaques are characteristic features of Alzheimer's disease. They lead to degeneration of the affected neurons. The cellular processes shown here takes place after the the amyloid beta peptide has been cleaved by the gamma and beta secretases. The amyloid residue leaves the cell membrane, changes shape and aggregates into long fibrils. These fibrils form dense plaques on nerve cells.