Pablo Moncada, Undergraduate Student - Larkin Laboratory, Department of Molecular and Integrative Physiology, UM Medical School and Department of Biomedical Engineering, UM College of Engineering
For the proper movement of our joints, muscles must be connected to bones, but directly connecting the relatively soft muscle tissue to the very hard bone tissue would result in tearing with movement. Therefore, an interface is needed; this is accomplished by tendons, which are fibrous in nature and capable of withstanding tension. This is an image of the junction between muscle and tendon, viewed through two polarized filters. Viewed without these filters, both tissues are the same color, but with the filters placed perpendicular to each other, the bright colors in the photo appear. This is caused by a property called birefringence, which splits light into two rays with slightly different paths. The muscle and tendon have different birefringence properties (the tendon is brighter); what we are seeing isn't the tissue itself, but its ability to bend light going through it.