Myelinated nerve. Light micrograph of a section through a peripheral myelinated nerve, showing many individual axons each covered with deep blue-staining myelin sheaths. Myelin is a lipid (fat)-rich layer of concentric plasma membranes that insulate the nerve and enhance the speed of nerve impulses. Cell nuclei mixed in between the axons are the Schwann cells which produce the myelin. The whole nerve fibre is enclosed by supporting tissue called the perineurium. Magnification: x150 when printed 10 centimetres wide.