Exogenous Zeitgebers Flashcards
External Environmental Factors That Reset Biological Clocks
-Resetting biological clocks is a process known as entrainment
-Without external cues, the free-running biological clock continues to ‘tick’ in a cyclical pattern. Zeitgebers reset the sleep/wake cycle (interaction of internal and external factors)
Light As Key Exogenous Zeitgeber
-Light can reset the body’s main endogenous pacemaker (SCN), and also has an indirect influence on key processes in the body controlling hormone secretion, blood circulation, etc.
-Campbell and Murphy woke 15 participants at various times and shone a light on the back of their knees- producing a deviation in the sleep/wake cycle of up to three hours. Light does not necessarily rely on the eyes to influence to SCN.
Social Cues
-The sleep/wake cycle is fairly random in human newborns, but most babies are entrained by about 16 weeks. Schedules imposed by parents are a key influence, including adult-determined mealtimes and bedtimes.
-Research on jet lag shows adapting to local times for eating and sleeping (not responding to one’s own feelings of hunger and fatigue) entrains circadian rhythms and tackles jet lag.
A03 (Exogenous Zeitgebers Differ In Different Environments.)
E- Exogenous zeitgebers do not have the same effects on people who live in places where there is very little darkness in summer and very little light in winter. For instance, the Innuit Indians of the Arctic Circle have similar sleep patterns all-year round, despite spending around six months in almost total darkness
E- This suggests the sleep/wake cycle is primarily controlled by endogenous pacemakers that can override environmental changes in light.
A03 (Case Study Evidence Undermines Effects Of Exogenous Cues)
E- Miles et al. reported the case of a man, blind from birth, with an abnormal circadian rhythm of 24.9 hours. Despite exposure to social cues, such as mealtimes, his sleep/wake cycle could not be adjusted.
E- This suggests that social cues alone are not effective in resetting the biological rhythm and natural body clock is stronger.
A03 (Age-Related Insomnia)
E- Natural changes in circadian rhythms mean older people fall asleep early and have poorer quality sleep. However, Hood et al. found that management of insomnia improved if older people were more active and had more exposure to natural light during the day.
E- This suggests that exogenous changes in lifestyle may be just as likely to cause age-related insomnia as internal, biological changes.
