Nerves, electric potential structure

Considerations of the physical features that could control the transport and permeability of ions in membranes need to take into account the transmembrane potential. This potential, as determined experimentally, corresponds to the difference in the electrical potentials between the two aqueous phases away from the inner and outer membrane surfaces, and its steady-state value is related to such factors as the difference in ionic concentrations of the two aqueous phases, ionic permeability of the membrane, and the presence of any fixed charges or dipolar species in the membrane structure. Excitable cells such as those of nerve or muscle tissue exhibit resting membrane potentials of up to 90 mV and greater, whereas many of the small and nonexcitable cells (e.g., erythrocytes) exhibit smaller values of around 20 mV or so. 

Electrodes are the direct interface between the biological structures (auditory neurons) and the electronic system in the CFs. Stimulation electrodes inject charge into the tissue to functionally excite the nerves by electrical stimulation. In other words, electrodes measure the electric potential for charge transfer between solid metal state and electrolyte solution in liquid state inside the cochlea. For better stability implants electrode properties must be evaluated with respect to a biocompatible application for optimum stability, efficacy and life time with a minimum of toxicity. From the material point of view the requirements of an ideal electrode [8-10] might be summarized as follows ... 

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