Computer simulation of the generation, propagation and extinction of a single fiber monopolar action potential.

Educational simulation of the generation, propagation and extinction of the surface monopolar action potential (AP) of a single fiber using the tripole model. The voltage scale is in arbitrary units. The x and y scales are in mm. The fiber is placed at 5 mm depth below the surface of an infinite half space having conductivities similar to those of the anisotropic muscle. The fiber is parallel to the skin and the tripole is 7 mm long. The fiber is 120 mm long with the neuromuscular junction at y=0, at 40 mm from the tendon ending T2 and 80 mm from the tendon ending T1 to show separate end-of-fiber effects. Observe the spatial extent of the voltage distribution on the surface, in particular during the end-of-fiber effects. This is reduced by the differential detection. A motor unit action potential (MUAP) is the algebraic summation of spatio-temporal contributions like this from the fibers of the MU and the sEMG is the algebraic summation of the MUAP trains of the active MUs. These summations result in a random-like signal.