Biological Voltages

There is an abundance of electrical phenomena associated with life processes. Associated with cells and the extracellular fluid are ions associated with the electrolytes such as chlorine Cl^-, potassium K⁺, and sodium Na⁺. Different concentrations of electric charge on the two sides of a cell membrane will produce an electric field across the membrane, which one can detect by measuring the voltage across the membrane. In biological literature it is common to refer to the voltage across the membrane as the "potential" or "membrane potential", so that the 90 millivolts measured across the membrane below may be referred to as the "resting potential" for the membrane. When the voltage is established across the membrane, the membrane is said to be "polarized", and the idea of polarization has wide application in bioelectricity. The polarization of a cell membrane can either assist or oppose the processes of diffusion and osmosis which arise from concentration differences.

The Cell membrane potentials are crucially important in the life of a cell, where sophisticated processes control the transport of materials both into and out of the cells.

For the nerve cell, this equilibrium is disturbed by the arrival of a suitable stimulus. The dynamic changes in the membrane potential in response to the stimulus is called an action potential. After the action potential the mechanisms described above bring the cell membrane back to its resting state.

Muscle action is controlled by electrical signals from the nervous system, where nerve signals can lead to a polarization of muscle fibers and contraction.

The polarization and depolarization of muscle fibers produces detectable signals in the form of electric fields which are measurable. The electric fields and measurable voltages associated with heart action have been very valuable for diagnostic purposes in electrocardiograms. The electrical processes in the brain are detectable in electroencephalograms. Even the electrical signals from other muscles of the body are detectable as electromyograms.