I am trying to get some background for some personal research I am doing into the effects of Electro Convulsive Therapy. I don't understand how electric current from an external household source, say, flows through the body. There are no naturally occurring chains of metal atoms in the body, so it can't be electron flow, but my understanding is that the electric field around an electrode is very thin, so I can't see ion flow as accounting for electrical effects in the body at some distance from the electode - particularly with AC, as I would only expect a local oscillation. I am familiar with membrane depolarisation but that is essentially a cellular mechanism - is it (or saltatory conduction) activated by an external current? I know that the body as a whole (and cell membranes in particular) function as a dielectric, but I can't see how this fits into the global picture of current flow between two electrodes. Can anyone help or recommend me a paper?
Electric current flows rather rather easily through water that contains ions, which are electrically charged atoms. Since the human body is more than half water, and that water is filled with ions such as sodium, chlorine, potassium, etc., the body for the most part conducts electricity rather well. The skin can have a high resistance to the flow of electricity, but it varies substantially, particularly being reduced when the skin is moist. Medical electrodes, as for heatbeat measurements, are typically applied with conductive paste to overcome most of the skin's resistance. You may want to look at this "Electricity And Human Body" page, or the article "Conduction of Electrical Current to and Through the Human Body: A Review".