any material agent, external or internal, conscious or unconscious, acting as a condition for subsequent changes in the state of the organism; any factor that affects the body and can cause a certain response; generic concept in relation to the concepts of mule and signal. In the presence of a fixed cause-and-effect relationship between a given event and subsequent changes in the state of the organism, the stimulus acts as a stimulus, and the corresponding change acts as a reaction. Stimuli are distinguished:
1) biogenic – directly biologically significant;
2) abiogenic – indirectly biologically significant;
3) with unrevealed, direct biological significance.