A nerve trunk (A) has an annular electrode cuff (B) positioned therearound for imposing electrical signals on to the nerve trunk for the purpose of generating unidirectionally propagated action potentials. The electrode cuff includes an annular cathode (30) having a circular passage therethrough of a first diameter. An annular anode (40) has a larger circular passage therethrough of a second diameter, which second diameter is about 1.2 to 3.0 times the first diameter. A non-conductive sheath (50) extends around the anode, cathode, and nerve trunk. The anode and cathode are placed asymmetrically to one side of the non-conductive sheath. Specifically, a first length (L1) along the electrode sheath between a first end (56) and the cathode is at least twice a second length (L2) between the anode and cathode. A third length (L3) between the anode and a second end (58) of the conductive sheath is smaller than the first or second lengths. With this geometry, the majority of the current applied to the anode electrode flows to the cathode along path segments (62b and 62d) with lesser amounts of current flowing in the path segments (64a), (64b), (66a), and (66b).