Anaysis of the spatial distribution of muscle fibers within the territory of a motor unit

The spatial distribution of muscle fibers belonging to a motor unit (MU) was studied in 3 soleus (Sol) and 4 tibialis anterior (TA) units in 7 adult cats. The purpose of this study was to provide a detailed description of the spatial patterns which exist over the entire motor unit territory. Glycogen depletion of the motor unit was achieved through repetitive stimulation of either the intracellularly identified motoneuron (Sol units) or the functionally isolated motor axon (TA units). A point-to-nearest neighbor analysis was performed to test for the existence of areas within the MU territory that were void of MU fibers. The distance between each MU fiber and all other MU fibers was calculated to provide information regarding the spacing between MU fibers. In all units, MU fibers tended to be localized to rather discrete regions of the muscle. The quadrat analysis revealed that MU fibers were not evenly distributed throughout their territory.