The cytoskeleton plays a key role in maintaining the highly asymmetrical shape and structural polarity of neurons that are essential for neuronal physiology. The cytoskeleton is made up of microfilaments, intermediate filaments and microtubules. Microfilaments (4-9 nm diameter) are made up of actin monomers and they function mainly to provide mechanical support and locomotion to the cell. Intermediate filaments are cytoplasmic fibers of ~10nm diameter. They provide supporting framework within the cell. Microtubules (~24nm diameter) consist of tubulin and microtubule associate proteins. They function to transport nutrients and chemical messengers along the cell. Neurofibrillary tangles are twisted bundles of neurofibrils formed when the microtubule-associated protein, tau, dissociates from microtubules and clusters to form an insoluble mass. Under normal conditions tau binds to microtubules, stabilizing neuronal structure and integrity.