Unmyelinated intestinal nerve fibre. Coloured transmission electron micrograph (TEM) of a section across an nerve fibre from the intestine. The nerve fibre (centre) is surrounded by smooth muscle cells. Several nerves are bundled together to form this nerve fibre, forming a plexus. This plexus controls peristalsis, the regular muscular contraction that moves food through the intestine. These intestinal nerves lack the fatty, insulating myelin sheath that is found around most nerves. Magnification: x7000 when printed 10 centimetres wide.