In part I, we had a brief overview of what qualities make a silver/silver chloride electrode useful. In this section, we’ll look at a few of the most common purposes that these pieces are put to.
Electromyograms, or EMGs, are devices that measure the electrical potential of a cluster of muscle fibers. A surface EMG, or sEMG, uses the ag/agcl electrode to connect to the skin on either side of a muscle cluster (as opposed to an intramuscular EMG, which skips the electrode and uses fine needles inserted into the fibers themselves.) A relaxed muscle has zero electrical potential; the more muscle fibers get involved in a muscular contraction, the higher the potential becomes.
sEMGs can thus be used to tell you when a muscle is twitching involuntarily and to what degree; how much of a muscle you’re using in a particular motion; whether or not a particular muscle is involved in an involuntary process such as keeping your balance, and so on. The medical potential of the sEMG is enormous.
Electroencephalographs, or EEGs, measure brain activity by recording the effects of neuron discharges on the electrical potential of the scalp in much the same way that sEMGs record muscle potential. EEGs allow us to study the goings-on of the brain without complex surgery. In this role, they have use in sleep studies, epilepsy studies, coma/brain death studies, brain tumors, and diagnosing a stroke.
Our bodies are capable of an extraordinary variety of conscious, deliberate movements, many of which we never actually use. One of the reasons why we don’t is that while the movements are possible, we frequently don’t have enough of a sense of when a particular muscle is being activated to be able to consciously select that muscle and activate it. That lack of sense can be replaced using a silver/silver chloride electrode and a biofeedback machine, in a simpler variation of the sEMG. By showing you plainly when your muscle is being used, you can begin to develop conscious control over it.
We hope you’ve enjoyed our exploration of the silver/silver chloride electrode — we’ve only scratched the surface, naturally. There are dozens of non-biomedical applications of the electrode as well, from the oceanographic record of electric fields to sensing corrosion on metal pipelines. Electrodes rule!