exogenous zeitgebers and the sleep/wake cycle

Question 1

exogenous zeitgebers definition

Answer 1

external factors that affect or entrain our biological rhythms, such as the influence of light on the sleep/wake cycle

Question 2

sleep/wake cycle definition

Answer 2

a daily cycle of biological activity based on a 24-hour period (circadian rhythm) that is influenced by regular variations in the environment, such as the alternation of night and day

Question 3

what are exogenous zeitgebers

Answer 3

external factors in the environment that rest our biological clocks through a process known as entrainment

Question 4

what did Siffre’s study show about sleep/wake cycle with no external cues

Answer 4

the free-running biological clock controls the sleep/wake cycle continues to ‘tick’ in distinct cyclical patterns

Question 5

how is the free running cycle entrained

Answer 5

by environmental cues so there is an interaction of internal and external factors

Question 6

Light as an exogenous zeitgeber

Answer 6

key exogenous zeitgeber in humans. can reset the body’s main endogenous pacemaker the SCN so therefore plays a role in the maintenance of the sleep/wake cycle

Question 7

light indirect influence of body processes

Answer 7

indirect influence of key processes in the body such as controlling such functions as hormone secretion and blood circulation

Question 8

who researched light as an exogenous zeitgeber

Answer 8

Campbell and Murphey 1998

Question 9

Campbell and Murphey aim

Answer 9

demonstrate that light may be detected by skin receptor sites on the body even when the same information is nor received by the eyes

Question 10

Campbell and Murphey procedure

Answer 10

-15 participants
-woken at different times and a light pad was shone on the back of their knees

Question 11

Campbell and Murphey findings

Answer 11

-produce a deviation on the participants usual sleep/wake cycle up to 3 hours in some cases
-suggests light is a powerful exogenous zeitgeber that need no necessarily rely on the eyes to exert its influence on the brain

Question 12

new born babies sleep/wake cycle

Answer 12

basically random

Question 13

circadian rhythm of babies

Answer 13

-6 weeks the circadian rhythms begin
-16 weeks babies rhythms have been entrained by the schedules imposed by parents, including adult-determined mealtimes and bedtimes

Question 14

jet lag on sleep/wake cycle

Answer 14

-adapting to local times for eating and sleeping (not responding to ones own hunger of fatigue) is effective way of entraining circadian rhythms and beating jet lag when travelling long distances

Question 15

limitation of exogenous zeitgebers - environmental observations

Answer 15

-do not have the same effects in all environments
-experience of people who live in places where there is very little darkness in summer and very light in winter tell a different story from the unusual narrative. for example, people living in the artic circle have similar sleep patterns all year round despite having 6 months of almost no natural light (darkness) –> suggest the sleep/wake cycle is primarily controlled by endogenous pacemakers that can override environmental changes in light

Question 16

limitation of exogenous zeitgebers- case study evidence

Answer 16

-evidence challenged the role of exogenous zeitgebers
-Miles et al 1977 recount the study of a young man, blind from birth, who had an abnormal circadian rhythm of 24.9 hours. despite exposure to social cues, such as regular mealtimes, his sleep/wake cycle could not be adjusted
–> suggests social cues alone are not effective in resetting in biological rhythm

Question 17

evidence of exogenous zeitgebers-age-related insomnia

Answer 17

-evidence suggests people have poorer sleep quality as they get older. this may be due to natural changes in the circadian rhythm as we age, which means falling asleep earlier and broken sleep at night (Duffy et al 2015)
-studies have suggested that exogenous factors may be more responsible for he changes in sleep patterns amongst older people. Hood et al 2004 found that management of insomnia was improved if elderly people were generally more active and had more exposure to natural light