All moral rights asserted. Recolouring or alteration of the image is prohibited without permission. Coloured scanning electron micrograph (SEM) of a freeze fracture through muscle tissue. The red units are muscle fibres, which have a striped appearance due to the many individual units of contractile filaments called myofibrils.. Each fibre is surrounded by endomysium connective tissue (white and blue) , which contains nerve cells and capillary blood vessels (yellow). Erythrocytes, or red blood cells, (bright red) can be seen in some of the capillaries. Magnification: x2500 when printed at 15 centimetres wide.