Bioelectric Phenomena

Bioelectric phenomena

The beginning of the study of electrical phenomena occurring in living tissues dates back to the 2nd half of the 18th century, when it was discovered that some fish (electric stingray, electric eel) use electrical discharges when hunting, stunning and immobilizing their prey. It has been suggested that the propagation of a nerve impulse is the flow of a special “electrical fluid” along the nerve. In 1791-1792 Italian scientists L. Galvani and A. Volta were the first to give a scientific explanation of the phenomenon of “animal electricity”. With their now classical experiments, they reliably established the fact of the existence of electrical phenomena in a living body. Later, bioelectric phenomena were discovered in plant tissues.

From the standpoint of modern ideas about bioelectric phenomena, it is clear that all life processes are inextricably linked with various forms of bioelectricity. In particular, bioelectric phenomena determine the occurrence of excitation and its conduction along nerve fibers, cause the processes of contraction of muscle fibers of skeletal, smooth and cardiac muscles, the excretory function of glandular cells, etc. Bioelectric phenomena underlie absorption processes in the gastrointestinal tract, the perception of taste and smell, the activity of all analyzers, etc. There is no physiological process in a living organism that is not associated with bioelectricity in one form or another.

But what exactly are bioelectric phenomena, where do they come from, what is their participation in life processes? To facilitate understanding of the essence of bioelectric phenomena, any living organism can be represented as a complex mixture of liquids and various chemical compounds. Many of these compounds (both those entering the body in the form of food, and those isolated from it during metabolism, and intermediate substances formed during metabolism) are in the form of positively or negatively charged particles - ions.

The redistribution of these ions and their transport, which constantly take place in the process of life, is the reason for the occurrence of bioelectric phenomena. In practice, all bioelectric phenomena are determined through the difference in electrical potential between two points of living tissue, which can be recorded by special electrical devices - galvanometers. Using microelectrodes, for example, it is possible to measure the potential difference between the outer and inner sides of the cell membrane (membrane).

This potential difference is called the resting potential, or membrane potential. Its presence is due to the uneven distribution of ions (primarily sodium and potassium ions) between the internal contents of the cell (its cytoplasm) and the environment surrounding the cell. The magnitude of the membrane potential is different: for a nerve cell it is 60-80 millivolts (mV), for striated muscle fibers - 80-90 mV, for cardiac muscle fibers - 90-95 mV, and for each type of cell at rest the potential value is strictly defined and reflects the intensity of metabolic processes occurring in this cell.

In an excited cell, another type of potential is recorded - the so-called action potential, which, unlike the resting potential, moves in the form of an excitation wave along the surface of the cell at a speed of up to several tens of meters per second. In each excited area, the potential acquires the opposite sign. The occurrence of an action potential is associated with a selective increase in the permeability of the cell membrane to sodium ions.

There are other types of potentials, in particular the so-called damage potential, or demarcation potential. This type of electrical activity is recorded between damaged and intact (undamaged) tissue areas. It can be assumed that its occurrence stimulates the recovery (regeneration) reserves of the cell (tissue).

Bioelectric phenomena (according to