| pseudospatial gradient sensing | <cell biology> Mechanism for sensing a gradient of a diffusible chemical in which the cell sends protrusions out at random, up gradient protrusions are stabilised by positive feedback (because receptor occupancy is rising with time) and others are transitory because of adaptation. Possibly the mechanism by which neutrophils sense chemotactic gradients. (18 Nov 1997) |
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| spatial sensing | Mechanism of sensing a gradient in which the signal is compared at different points on the cell surface and cell movement directed accordingly. Translocation of all or part of the cell is not required. See: temporal gradient sensing, pseudospatial gradient sensing. (18 Nov 1997) |
| temporal sensing | <technique> Mechanism of gradient sensing in which the value of some environmental property is compared with the value at some previous time, the cell having moved position between the two samplings. Initial movement is random, until the second observation is made the gradient cannot be detected. See spatial and pseudospatial sensing mechanisms. Bacterial chemotaxis (so called) is based on this mechanism. (18 Nov 1997) |
| absolute intensity threshold acuity | The minimal light that can be seen. (05 Mar 2000) |
| absolute threshold | The lowest limit of any perception whatever. Compare: differential threshold. Synonym: stimulus threshold. (05 Mar 2000) |
| achromatic threshold | Threshold of visual sensation, the minimal light intensity evoking a visual sensation. Synonym: achromatic threshold, minimum light threshold. (05 Mar 2000) |
| anaerobic threshold | The oxygen consumption level above which aerobic energy production is supplemented by anaerobic mechanisms during exercise, resulting in a sustained increase in lactate concentration and metabolic acidosis. The anaerobic threshold is affected by factors that modify oxygen delivery to the tissues; it is low in patients with heart disease. Methods of measurement include direct measure of lactate concentration, direct measurement of bicarbonate concentration, and gas exchange measurements. (12 Dec 1998) |
| auditory threshold | The audibility limit of discriminating sound intensity and pitch. (12 Dec 1998) |
| brightness difference threshold | The smallest difference that can be perceived as a difference in brightness. Synonym: light difference. (05 Mar 2000) |
| pain threshold | Amount of stimulation required before the sensation of pain is experienced. (12 Dec 1998) |
| galvanic threshold | The minimal strength of an electrical stimulus of indefinite duration that is able to cause excitation of a tissue, e.g., muscle or nerve. See: chronaxie. Synonym: galvanic threshold. Origin: rheo-+ G. Basis, a base (05 Mar 2000) |
| relational threshold | The smallest degree of difference between two stimuli that permits them to be perceived as different. (05 Mar 2000) |
| visual threshold | Threshold of visual sensation, the minimal light intensity evoking a visual sensation. Synonym: achromatic threshold, minimum light threshold. (05 Mar 2000) |
| renal threshold | Concentration of plasma substance above which the substance appears in the urine. (05 Mar 2000) |
| phenotypic threshold | A quantitative genetic trait with a continuous distribution termed its liability may generate two kinds of phenotype, according to whether the liability lies above or below some critical threshold at about which a radical change in behaviour occurs. For instance, blood uric acid level is a liability with an approximately gaussian distribution. At a critical point of chemical saturation (the threshold crystallization occurs and the resulting gout or nongout is a threshold trait. (05 Mar 2000) |