Normal muscle tissue. Coloured scanning electron micrograph (SEM) of a section through healthy muscle tissue, showing the interior of a mitochondrion (purple) inside a muscle cell (myocyte). Mitochondria are highly specialised cells that produce the energy necessary for normal bodily functions. Muscle cells contain a great number of mitochondria embedded in myofibrils (red). Magnification: x9000, when printed 15 centimetres wide.