Peripheral nerve bundle. Coloured scanning electron micrograph (SEM) of a freeze-fractured sample of tissue containing a peripheral nerve bundle (centre). Within the bundle, single nerve fibres (blue) are surrounded by myelin sheaths (pale blue). These are formed by the Schwann cells (red). Also forming the bundle are reticular fibres (grey), a form of connective tissue. The nerve bundle is surrounded by perineural cells (yellow), with a cell nucleus (orange) at lower centre. Peripheral nerves are those outside the central nervous system (CNS). Magnification: x4700 when printed at 10 centimetres across.