Neurofilaments can be defined as the intermediate or 10nm filaments found in specifically in neuronal cells. In the electron microscope neurofilaments appears as 10nm diameter fibres of indeterminate length which generally have fine wispy protrusions from their sides. They are found particularly abundantly 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. They are composed a mixture of subunits which usually include the three neurofilament triplet proteins, known as NF-L, NF-M and NF-H. Neurofilaments may also include smaller amounts of peripherin, a-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.