Ultrastructural characteristic of the teleostean muscle fibers and their nerve endings. The stickleback (Gasterosteus aculeatus L.).

In myotome of the stickleback four muscle fibers types were distinguished. These comprised tonic, intermediate thin, intermediate thick and white muscle fibers. All the distinguished fibers varied in regard to ultrastructural organization of their sarcomeres, T systems location and myoneural junction. The sarcomeres of both intermediate and white muscle fibers contained all the three classes of myosin filaments: 12 nm, 19 nm and 25 nm in diameters. However, the sarcomeres of tonic muscle fiber are built of the 25 nm thick myosin filaments only. The nerve endings attached to the particular fibers varied also in composition of the synaptic vesicles classes which they contained.