Trigger (system theory)
A trigger is a process that influences the behavior of a system from outside (through information, messages, stimuli, inputs) . The reaction takes place immediately or after processing by the system: A system changes from one state (Z1) to another state (Z2) through a triggering process. There is no other transition option, such as B. from Z1 to Z3. (In contrast, see the control and regulation of a system.)
Properties of a trigger
The energy of the triggering process is not included in the energy balance of the triggered process.
The type and direction of the triggered reaction are not influenced by the trigger, but are specified by the system.
However, in many cases a minimum amount of energy has to be expended in order to overcome the internal resistance of the system. If this threshold is exceeded, however, the transition takes place completely and in its maximum strength. This is also known as the all-or-nothing principle , as it is used in biology e.g. B. is to be found when triggering an action potential of a nerve cell .
After triggering, the initial state of the system can be reached (automatically) without external influence (example: monosynaptic reflex , modern camera, automatic weapons) or must be restored from the outside. Triggering is only possible as long as there are enough resources to restore the initial state.
A trigger must also be channel-specific: the system must be receptive to the trigger. (The visual cells of the human eye are only receptive to electromagnetic waves with a wavelength between 400 and 800 nm.)
More options
It is possible that a system can react to different triggers with the transition from Z1 to Z2. (In this way, the photoreceptor cells in the retina react not only to light, but also to a stroke.)
In more complex systems, different triggers can cause different reactions, but each trigger is assigned its own transition: A1 triggers the transition from Z1 to Z2, A2 that from Z1 to Z3 etc. ( See the concept of the innate triggering mechanism of ethology , where each key stimulus ) is assigned its own behavior.
Examples :
- A ticket machine requires several pieces of information in order to print out a specific ticket.
- In the case of a polysynaptic reflex, depending on the strength of the stimulus, the reaction becomes stronger and stronger, as more and more executive organs are switched on (clearing the throat - coughing - choking cough )
Examples of triggers
- A spark triggers an explosion .
- A tremor in the snowpack triggers an avalanche .
- A scream triggers panic .
- A light quantum triggers a signal chain in the sensory cells of the retina of the eye.
- A brief stretching of the lower leg lifter triggers its contraction ( hamstring reflex ).
- A slight pressure on the trigger triggers the shot of a rifle .
- Allergens are triggers for allergies .