Fig. 5. Ultrastructural analysis of satellite cells in normo- and simulated microgravity conditions. Satellite cells without degeneration sign in normogravity (a,b); small mononuclear cell (c); myotube in formation (d); cytoplasm of a myotube characterized by numerous filaments (arrows), such as neoformation of sarcomeric structures (e); multinucleated myotube (f). In simulated microgravity, myotubes (g,h) and mononuclear cells (i) with evident signs of cell degeneration: in particular, myotubes showed numerous lipofuscin granules with electrondense cytoplasm (arrows) and without the common cell organelles.