Figure 1: Cross (a) and longitudinal (b) sections of muscle fibers from the mouse EDL muscle. In (a), slender, elongated approximately cylindrical mitochondria profiles occupy the intermyofibrillar spaces, running transversely for long distances between the myofibrils at the I band level. In (b), the longitudinal axis of the fiber runs from left to right at a slight angle. Longitudinally arranged mitochondria send out transverse branches at the level of the I band, that correspond to those seen in (a). The transverse mitochondria branches run parallel to triads (CRUs) and are closely opposed to the junctional SR (arrows) over long distances.