Myelinated nerve fibres. Light micrograph of a section through a spinal sensory nerve containing many closely packed axons exhibiting a wave-type appearance. The green stain represents the axons themselves and their covering of myelin, the fatty-rich tissue sheath that facilitates rapid conduction of nerve impulses essential in most neural sensory systems. Myelin sheaths are produced by Schwann cells whose nuclei can be seen in large numbers along the nerve fibres. Schwann cells are not neurons but provide essential structural and functional support for the nerves with which they are intimately associated. Magnification: x180, when printed 10 centimetres high.