Tissue DC Properties

The Nemst equation (Eq. 7.9) defines potential differences as a function of ionic activities, and the Maxwell/Gauss equation defines potential changes as a function of charge densities. We may hypothesize that there are DC potential differences between some of the 

On the surface of the body, DC recording is moreover used in electro-oculography to determine the position of an eye behind a closed eyelid. Together with GSR, this is one of the few electrophysiological methods making use of DC potentials. 

Remember that with an exogenic DC source, it is not possible from a pure DC measurement to discern between changes in EMVs and resistance/conductance (cf.. Section 7.9.1). Measiu-ed DC voltage is not necessarily proportional to the DC resistance of the unknown if a DC constant crurent is passed through the unknown. 

As explained, there are endoelectrogenic soiu-ces in the cell membranes. However, it is quite likely that some macroscopic membranes around organs are also the sites of electricity sources. Nordenstr0m (1983) proposed that there are closed DC circuits in the body with the well-conducting blood vessels serving as cables (e.g., a vascular-interstitial closed circuit). These DC currents can cause electro-osmotic transport through capillaries. Dental galvanism is the production of electricity by the metals in the teeth. 

Living tissue is surrounded by extracellular liquids, and these liquids have a DC conductivity of approximately 1 S/m, Section 4.2.1. However, all organs in the body are 

---