The healthy human brain consists of billions of neurons. These neurons process the information and transmit the information in the form of various chemical and electrical signals. The neurons help exchange the information between the various parts of the brain, and between brain and the various parts of the body through the peripheral nervous system. The Alzheimer's disease disrupts this communication, resulting in the loss of function of neurons and eventual death of the neuronal cells.
Neurofibrillary tangles are abnormal accumulation of the tau proteins inside the neuron. The tau proteins are present in the ends of the microtubules that form the skeleton of the neurons. When the tau proteins detach from the microtubules and agglomerate, it leads to the tangling of the microtubule fibres inside the cell. This tangle hampers the transmission of signal through the body of the neuron.