PERIPHERAL NERVE AND MUSCLE STIMULATION

In this chapter we focus on technology to activate peripheral motor nerves electrically. Two important concepts are stressed: 1) the closer the electrode is to the target tissue the easier it is to isolate the applied electric field to a smaller region, and 2) the effect of the applied electric field is, generally speaking, always the greatest on the largest myelinated axons experiencing the applied electric field. These concepts are applicable to other neural systems. Motor nerves can be activated through electrodes placed on the surface of the skin, on the surface of the muscle, in the muscle, on the motor nerve, or in the motor nerve. All electrodes must satisfy the requirements of material compatibility, mechanical compatibility and the ability to transfer the required electrical charges without tissue or material deterioration. The choice of electrode materials and geometric design are determined by these factors and by the intended location on the nerve or muscle. Specific designs, tissue reactions, and applications are described herein. Electrodes placed on muscles produce single muscle activation. Nerve electrodes can have the advantage of activating multiple muscles. Selective stimulation of peripheral nerve fibers for effecting specific muscle activation or specific motor function is discussed in the section on nerve electrodes.