Deformities that develop within neurons that prevent them from functioning properly. The body of a neuron contains numerous tiny fibers, called neurofibrils, that conduct electrical impulses through the cell. Typically, neurofibrillary tangles form around abnormal protein deposits that collect in the cell’s cytoplasm, such as the tau deposits (amyloid plaques) that are characteristic of Alzheimer’s disease and progressive supranuclear palsy (PSP), and the alpha-synuclein deposits called lewy bodies that are characteristic of Parkinson’s disease. Neurofibrillary tangles interfere with the neuron’s ability to shuttle nutrients, raw materials, waste, and its end product neurotransmitters to the appropriate places and organelles within itself, greatly impairing the neuron’s ability to function. This disrupts neuron communication in the nervous system. Scientists are not certain whether neurofibrillary tangles form as a consequence of other biochemical factors involved in the disease process or are themselves part of that process.