The motor-sensory unit system (Figure 129.1) refers to the alpha motor unit, the gamma motor unit, the sensory nerve fibers that carry information from the intrafusal fiber back to the alpha motor neurons, and the Renshaw cell.

Figure 129.1.— Schematic representation of the motor-sensory unit system. AMN: alpha motor neuron; RC: Renshaw cell; DGC: dorsal ganglion cell; EFMF: extrafusal motor fiber; IFMF: intrafusal motor fiber; GMN: gamma motor neuron. Arrows indicate direction of conduction.