BIOELECTRODE

Bioelectrodes function as an interface between biological structures and electronic systems. Electrical activity within the biological structure is either sensed or stimulated. The electrical systems are either passively sensing (measuring) or actively stimulating (inducing) electrical potentials within the biological structure or unit.

Electrical currents are generated by many biological structures. Currents give rise to potential differences that can be measured using electrodes and can be interpreted to gain insight in the functioning of the source structure. Conversely, current can be applied to the biological structure through electrodes to affect the target.

The same electrode may function either passively or actively, depending on the purpose and the electronic system controls. An example seen on TV is the large defibrillation paddles used by paramedics to resuscitate people in cardiac distress. When the paddles are applied to a patient, the electrical system is programmed to first passively sense the electrical activity (or lack of) within the heart. Then the electrical system uses algorithms to determine if a stimulation (shock) is required, and finally to provide the appropriate electrical stimulation.

The size of bioelectrodes ranges from microscopic intra-cellular research electrodes to large (3 x 5-inch) defibrillation paddles.

Most bioelectrodes are made of metal, but the microscopic intra-cellular research electrodes are glass capillary tubes filled with a conductive saline solution.

The following table gives some examples of applications, characteristics, and materials.

* has a conductive gel applied
Perhaps one of the most infamous applications of bioelectrodes is the “Electric Chair,” used for executing criminals in certain localities. A voltage is applied with so much power that the nervous system, including the pacing of the heart, are overwhelmed and cease to function, causing death.
Neurophysiology techniques are used to measure variations in electrical potentials for understanding the pathways and functions of the nervous system. Bioelectrodes provide the interface.