AbstractThe study and description of a separated cell type have been dependent on the evolution of the electron microscope. There have been few experiments designed to induce changes in myonucleus and satellite‐cell populations in vivo without physically injuring muscle. In this regard, the most practical method to experimentally alter myonucleus and satellite‐cell populations is denervation. The sciatic nerve was sectioned in order to observe myonuleus and satellite‐cell behavior. After 7, 16, and 38 weeks postdenervation, the soleus and extensor digitorum longus muscles were observed under electron microscopy. In each studied period, the pattern, distribution, and possible cellular alterations were observed in the studied muscles. Myonuclei exhibited alterations such as shrinkage, nuclear membrane separation, condensed chromatin, ghost nuclei as well as normal ones, and disorganized myofibrils. The maximum and minimum myonucleus diameters were measured in each studied period. In both muscles, the maximum diameters decreased. On the other hand, the minimum myonucleus diameters did not show any differences. Regarding satellite cells, activation characteristics were observed. In both muscles, the satellite cells were located distant of capillary after denervation. Characterization of the different types of nuclei abnormalities, especially in chromatin condensation, should provide useful information for future morphological studies. © 2006 Wiley‐Liss, Inc. Microsurgery, 2006.