Neurofilaments can be defined as the intermediate or 10nm filaments found in specifically in neuronal cells. When visualised using an electron microscope, neurofilaments appear as 10nm diameter fibres of indeterminate length that generally have fine wispy protrusions from their sides. They are particularly abundant in axons of large projection neurons. They probably function to provide structural support for neurons and their synapses and to support the large axon diameters required for rapid conduction of impulses down axons. Neurofilaments are composed of a mixture of subunits, which usually includes the three neurofilament triplet proteins neurofilament light (NFL), neurofilament medium (NFM) and neurofilament heavy (NFH). Neurofilaments may also include smaller amounts of peripherin, alpha internexin, nestin and in some cases vimentin. Antibodies to the various neurofilament subunits are very useful cell type markers since the proteins are among the most abundant of the nervous system, are expressed only in neurons, and are biochemically very stable. Some studies have shown that levels of neurofilament heavy and neurofilament light are elevated in patients with Alzheimer's disease, frontotemporal lobe dementia, and vascular dementia.