| alternating current | Electrical current which alternates direction periodically. (For instance, household electric current is AC alternating at 60 oscillations/sec (60 Hertz) in the United States, and 50 Hertz in many other countries.) Acronym: AC (09 Oct 1997) |
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| alternating light test | Test to detect a relative afferent defect in one eye by watching pupillary movements. With the patient fixing in the distance, the light is held on each eye for about a second, and quickly moved to the other eye. Assuming no defect of the innervation to the iris sphincter in one eye (which would produce an anisocoria in light), the eye with the weaker light response has a relative afferent pupillary defect. This asymmetry of pupillomotor input can be estimated by holding neutral density filters in front of the better eye until the pupillary responses of the two eyes are balanced. Synonym: swinging light test. (05 Mar 2000) |
| alternating mydriasis | Mydriasis alternately affecting each eye. (05 Mar 2000) |
| alternating pulse | Mechanical alternation, a pulse regular in time but with alternate beats stronger and weaker, often detectable only with the sphygmomanometer and usually indicating serious myocardial disease. Synonym: pulsus alternans. (05 Mar 2000) |
| alternating strabismus | A form of strabismus in which either eye fixes. (05 Mar 2000) |
| alternating tremor | A form of hyperkinesia characterised by regular, symmetrical, to-and-fro movements (at about 4 per second) that are produced by patterned, alternating contraction of muscles and their antagonists. (05 Mar 2000) |
| action potential | <physiology> The sequential, electrochemical polarization and depolarisation that travels across the membrane of a nerve cell (neuron) in response to stimulation (touch, pain, cold, etc.) (09 Oct 1997) |
| bioelectric potential | Electrical potential's occurring in living organisms. (05 Mar 2000) |
| biological hazard potential | <radiobiology> Measure of the hazard posed by a given quantity of radioactive material in which the variation in biological effects of the various elements are accounted for. See: integrated biological hazard potential. (21 Mar 1998) |
| biotic potential | <biology, ecology> The potential growth a population of living things can expect if it were living under ideal environmental circumstances. (19 Jan 1998) |
| body surface potential mapping | Recording of regional electrophysiological information by analysis of surface potentials to give a complete picture of the effects of the currents from the heart on the body surface. It has been applied to the diagnosis of old inferior myocardial infarction, localization of the bypass pathway in wolff-parkinson-white syndrome, recognition of ventricular hypertrophy, estimation of the size of a myocardial infarct, and the effects of different interventions designed to reduce infarct size. The limiting factor at present is the complexity of the recording and analysis, which requires 100 or more electrodes, sophisticated instrumentation, and dedicated personnel. (12 Dec 1998) |
| brain potential | <physiology> The electrical charge of the brain as compared to a point on the body; the potential may be steady (DC potential) or may fluctuate at specific frequencies when recorded against time, giving rise to the electroencephalogram. (05 Mar 2000) |
| pacemaker potential | The voltage inscribed by impulses from an artificial electronic pacemaker. (05 Mar 2000) |
| generator potential | Local depolarisation of the membrane potential at the end of a sensory neurone in graded response to the strength of a stimulus applied to the associated receptor organ, e.g., a pacinian corpuscle; if the generator potential becomes large enough (because the stimulus is at least of threshold strength), it causes excitation at the nearest node of Ranvier and a propagated action potential. (05 Mar 2000) |
| receptor potential | The transmembrane potential difference of a sensory cell. Such cells are not generally excitable, but their response to stimulation is a gradual change in their resting potential. (18 Nov 1997) |