The localization of axon branchings in two muscle nerves of the rat. A contribution to motor unit topography.

The distribution of fiber branching in the proximal intramuscular motor nerves of the gracilis and gastrocnemius muscles of the rat was studied in whole-mount preparations of teased nerves. Branchings of nerve fibers were clustered at fascicular divisions. Such concurrence of fascicular and fiber branchings determines the dispersion of the single muscle fibers belonging to a motor unit. The distribution of fiber branching reveals the wiring pattern of muscle fibers. These patterns differed for the gracilis and gastrocnemius muscles in correspondence with their functional organization.