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In physiology, a stimulus [1] is a change in a living thing's internal or external environment. This change can be detected by an organism or organ using sensitivity, and leads to a physiological reaction. [ 2 ]
Stimulation, in general, refers to how organisms perceive incoming stimuli. As such it is part of the stimulus-response mechanism. Simple organisms broadly react in three ways to stimulation: too little stimulation causes them to stagnate, too much to die from stress or inability to adapt, and a medium amount causes them to adapt and grow as they overcome it.
Animals exhibiting, or responding to, characteristics that represent a supernormal stimulus usually display them as a result of selective pressures.Co-evolution between animals displaying supernormal stimuli, and the organisms responding to the supernormal stimuli, rely on evolution and propagation of genetics, behavioral patterns, and other biological factors. [4]
Taxes are classified based on the type of stimulus, and on whether the organism's response is to move towards or away from the stimulus. If the organism moves towards the stimulus the taxis are positive, while if it moves away the taxis are negative. For example, flagellate protozoans of the genus Euglena move towards a light source.
The stimulus is automatically decreased in steps of a set percentage until the response falls below the target (generation of an action potential). Thereafter, the stimulus is stepped up or down depending on whether the previous response was lesser or greater than the target response until a resting (or control) threshold has been established.
Kinesis, like a taxis or tropism, is a movement or activity of a cell or an organism in response to a stimulus (such as gas exposure, light intensity or ambient temperature). Unlike taxis, the response to the stimulus provided is non-directional.
The stimulus modality for vision is light; the human eye is able to access only a limited section of the electromagnetic spectrum, between 380 and 760 nanometres. [3] Specific inhibitory responses that take place in the visual cortex help create a visual focus on a specific point rather than the entire surrounding. [4]
In biology, a tropism is a phenomenon indicating the growth or turning movement of an organism, usually a plant, in response to an environmental stimulus. [1] In tropisms, this response is dependent on the direction of the stimulus (as opposed to nastic movements, which are non-directional responses).