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A number of examples of positive feedback systems may be found in physiology. One example is the onset of contractions in childbirth , known as the Ferguson reflex . When a contraction occurs, the hormone oxytocin causes a nerve stimulus, which stimulates the hypothalamus to produce more oxytocin, which increases uterine contractions.
The Hodgkin cycle represents a positive feedback loop in which an initial membrane depolarization leads to uncontrolled deflection of the membrane potential to near V Na. The initial depolarization must reach or surpass a certain threshold in order to activate voltage-gated Na + channels .
This bistability is most obvious in the transition between the follicular and luteal phases, and arises from interactions between positive and negative feedback loops involving GnRH, LH, FSH, estrogen, and progesterone. The kisspeptin system creates a switch-like mechanism driving the transition from negative to positive feedback.
Because all brain areas are bidirectionally coupled, these connections between brain areas form feedback loops. Positive feedback loops tend to cause oscillatory activity where frequency is inversely related to the delay time. An example of such a feedback loop is the connections between the thalamus and cortex – the thalamocortical radiations.
Low-T3 syndrome and high-T3 syndrome: Consequences of step-up hypodeiodination, e.g. in critical illness as an example for type 1 allostasis, [20] or hyperdeiodination, as in type 2 allostasis, including posttraumatic stress disorder. [12] Resistance to thyroid hormone: Feedback loop interrupted on the level of pituitary thyroid hormone receptors.
A vicious circle (or cycle) is a complex chain of events that reinforces itself through a feedback loop, with detrimental results. [1] It is a system with no tendency toward equilibrium (social, economic, ecological, etc.), at least in the short run. Each iteration of the cycle reinforces the previous one, in an example of positive feedback. A ...
An example of positive feedback is when a microphone picks up the sound that it is producing through a speaker, which is then played through the speaker, and so on. In addition to feedback, cybernetics is concerned with other forms of circular processes including: feedforward, recursion, and reflexivity.
An example is a system in which a protein P that is a product of gene G "positively regulates its own production by binding to a regulatory element of the gene coding for it," [14] and the protein gets used or lost at a rate that increases as its concentration increases. This feedback loop creates two possible states "on" and "off".