The Evolution of the Mitochondria-to-Calcium Release Units Relationship in Vertebrate Skeletal Muscles
Figure 3
Breast muscle from the finch shown in cross-sections (a) and (b). In the finch, as in other birds, mitochondria are located in single longitudinally oriented rows between the myofibrils. A limited proximity between mitochondria and CRUs (arrows in (b)) occurs where the mitochondria cross the level at which T tubules are located. Accumulations of mitochondria at the fiber edges are not present in the flight muscles of many birds, indicating that the mitochondria are not free to escape from the myofibrillar domains of the fibers, probably due to tethering; see Figure 2.
