Question 54-1 : Stress ? [ Concept english ]

Dark adaptation is an independent process during which each eye adjusts from a high luminance setting to a low luminance setting the exact mechanisms are unclear but they are known to include biochemical physical and neural both rods and cones contain light sensitive chemicals called photopigmentsthe photopigment in the rods is called rhodopsinthere are three different types of cone photopigments that are composed of opsins only slightly different from rhodopsin upon exposure to light photopigments undergo a chemical reaction that converts light energy to electrical activity initiating visual impulses in the retina that are conducted by nerve fibers from the eye to the brainthe initial chemical reaction is called light adaptation and in this process the photopigments are decomposed intense light will decompose the photoreceptor pigments rapidly and completely thus reducing retinal sensitivity to dim light regeneration of the photopigments occurs during dark adaptationthe fully dark adapted eye in which photopigment regeneration is complete restores retinal sensitivity to its maximal level rods and cones differ markedly however in their rate of dark adaptation cones attain maximum sensitivity in 5 7 minutes while rods require 30 45 minutes or longer of absolute darkness to attain maximum sensitivity after exposure to bright lightthe cones have a faster rate of photochemical regeneration because they function in greater light than the rods the cones however do not achieve the same level of sensitivity as the rods the rods slowly adapt to dim illumination but eventually achieve a much greater sensitivity than the conesdepending on the preadaptation to light dark adaptation is about 80% complete within 30 minutes but it may take hours or even days to acquire total dark adaptation

The cones detect colour vision and the fovea therefore gives us great resolution colour vision at normal every day light levels for things we are looking directly at

It takes about a day to shift one time zone the internal circadian clock adapts slowly to abrupt changes of time cuesthe rate of adaptation has been reported to follow a number of models rates of one hour per day without countermeasures or quicker adaptation during the first days have all been quotedhowever since the adaptation is highly dependent on the individual to the direction of flight to the number of time zones crossed to exposure to environmental cues any simplistic formula is inappropriatethe direction of the time zone change is particularly importantin general adaptation after eastbound travel is much slower than after westbound flight

It is important to understand that carbon monoxide poisoning can only occur if a person is in the presence of a source of the gasin fact the symptoms of carbon monoxide poisoning are often difficult to recognize because they resemble symptoms of other health problemsyou can suspect carbon monoxide poisoning when one or more people are in a place where there is a source of carbon monoxide these people experience symptoms the symptoms subside or disappear once the people leave the areathe main symptoms of a light poisoning are headache fatigue nausea vomitingsymptoms of a more serious poisoning are dizziness chest pain problems with vision difficulty concentratingsymptoms of an severe poisoning are problems coordinating movement or muscle paralysis which prevent the person from leaving the premises loss of consciousness