False-colour transmission electron micrograph (TEM) showing the myelin sheath surrounding the human auditory nerve. In longitudinal section, concentric layers of myelin sheath appear as orange bands at top of image. The layers are formed by envelopes of the cytoplasm of schwann cells (specialised cells which envelope all axons support). Myelination begins during foetal development with the introduction of a mesaxon (invagination of single nerve fibre into schwann cell) which wraps around the axon (evident towards bottom of image - blue area is axon). Magnification: X 88,000 at 35mm size. N.B. In all nerve fibres, the rate of conduction