AO1

• exogenous zeitgebers are external factors in the environment that reset our biological clocks through a process called entrainment
• in the absence of external cues the free running biological clock continues to tick in a distinct cyclical pattern
• light can reset the SCN and therefore plays a role in the maintenance of the sleep/wake cycle
• light has an indirect influence on key processes in the body that control such functions such as hormone secretion and blood circulation
• Campbell and Murphy demonstrated that light may be detected by skin receptor sites on the body even when the same information is not received by the eyes
• fifteen participants were woken at various tomes and a light pad was shone on the back of their knees
• The researchers managed to produce a deviation in the participants usual sleep/wake cycle of up to 3 hours in some cases
• at about 6 weeks of age the circadian rhythms begin and by about 16 weeks babies rhythms have been entrained by the schedules imposed by parents including adult determined mealtimes and bedtimes
• research on jetlag suggests that adapting to local times for eating and sleeping is an effective way of entraining circadian rhythms and beating jet lav