Biological Rhythms Flashcards
What are the three classifications of biological rhythms?
1) Circadian rhythms - cycles that generally occur once every 24 hours, e.g. sleep-wake cycle,
2) Infradian rhythms - cycles that occur less than once every day, e.g. menstrual cycle,
3) Ultradian rhythms - cycles that occur more than once every 24 hours, e.g. sleep cycle has several repeating stages of light and deep sleep.
What are endogenous pacemakers?
- Biological, internal, influences on biological rhythms, in example:
1) Some aspects of our biological rhythms are set by genetically determined structures and mechanisms within the body,
2) The suprachiasmatic nucleus, part of the hypothalamus, seems to act as an internal clock to keep the body on an approximate 24-hour sleep-waking cycle,
3) It is sensitive to light and regulates the pineal gland, which secretes melatonin.
Siffre (1962), method and findings
- Descended into a cave on July 16th 1962 completely devoid of natural light,
- He finished his experiment on September 14th, believing that it was August 20th,
- His sleep-wake cycle did not conform to a cyclical 24-hour clock, but was around 24-hours and 30-minutes, with Siffre determining when to sleep and when to eat,
- Demonstrates a free-running circadian rhythm, one not affected by exogenous zeitgebers,
- This demonstrates the effect prolonged exposure to a strong exogenous zeitgeber such as light.
Sabbagh and Barnard (1984), findings
Found that when women live together their menstrual cycles may synchronise. The reason for this is unknown.
Menaker et al. (1978), findings
Caused brain lesions of the suprachiasmatic nucleus, part of the hypothalamus, in hamsters - their sleep schedule was disrupted.
Pengelly and Fisher (1957) findings? What did this show?
Found that squirrels will hibernate even when kept in laboratory conditions very different from their natural environment. Proves that, in some cases, endogenous factors may completely determine a cycle.
An example of cultural factors effect endogenous and exogenous pacemakers/zeitgebers?
Inuits often live in permanent daylight or permanent night-time but can maintain regular daily sleep cycles - so the cycle can’t just be determined by levels of light acting on the pineal gland.
What did Dr. Espie find?
- Circadian rhythms may not and do not always have to conform to cyclical 24-hour periods,
- Delayed the starting time of Monkseaton high school to 10AM, instead of the usual 8AM,
- Researchers note that GCSE results went up from 34% of pupils scoring 5 A* - C grades including English and Maths, to 53%,
- For disadvantaged students, the rates of scoring 5 A* - C grades increased from 12% to 42%,
- SHows that circadian rhythms hinge on individual differences: e.g. teenagers compared to adults.
Aschoff and Wever (1967), method
55 participants deprived of natural light whilst spending 4 weeks in an underground bunker.
Aschoff and Wever (1967), findings
Found that in a group of people isolated from daylight, some maintained their regular sleep-wake cycles. Other members of the group displayed their own very extreme idiosyncrasies, e.g. 29 hours awake followed by 21 hours asleep. This also shows that factors must interact to control or influence biological rhythms.
- 36 subjects remained internally synchronised during the whole experiment,
- All participants showed free-running circadian rhythms.
What in the modern world effects exogenous zeitgebers? What is the consequence?
- In the natural environment, zeitgebers normally change slowly,
- However, in the modern world, zeitgebers can change quickly. This can have negative effects on our ability to function - slowing reaction times, impairing problem solving skills, and limiting our ability to concentrate.
What are exogenous zeitgebers?
- Influences from outside the body that act like a prompt, which may trigger a biological rhythm, e.g. light.
How does jet lag effect biological rhythms?
- Flying on a jet allows travel to different time zones,
- Consequently you’ll feel sleepy at an earlier/later local time. If you then went to sleep you would wake-up earlier/later and end up out of sync with local timing. It appears easiest to adapt by forcing yourself to stay awake/or to go to sleep,
- It can take about a week to fully synchronise to a new time zone.
Wegman et al. (1986), findings
Found that travelling east to west (phase delay) seems easier to adapt than travelling west to east (phase advance).
Schwartz et al. (1995), findings
Found that basketball teams from the east coast of the USA got better results travelling to play in the west than the west playing in the east.
What is another modern impact on sleep cycles?
Shift-work; working in the early hours of the morning or late at night.
Czeisler et al. (1982), method and findings?
Studied workers at a factory whose shift patterns appeared to cause sleep and health problems. The researchers recommended 21-day shifts, allowing more time for workers to adapt, and changing shifts forward in time (phase delay). After implementing these changes, productivity and jobsatisfaction increased.
Evaluations of research on biological rhythms?
- Findings from animal studies cannot be accurately generalised to the human population; humans have greater adaptability,
- Studies that have deprived humans of natural light have still allowed artificial light, which may give many of the benefits of natural light,
- Things like individual differences need further study. Some people are more alert early in the day, and others later on, and the speed with which we adapt to disruptions can vary. It is difficult to determine whether a person’s lifestyle is a cause or effect of their biological rhythms,
- If we fully understand what causes the problems linked to jet lag and shift work, we can minimise and avoid them, reducing accidents in work environments. There are different ways to deal with these problems, e.g. taking time to naturally adjust, or using drugs to reduce the effects of sleep deprivation.
What did McClintock et al. (1998) demonstrate?
- Demonstrated menstrual cycle synchronisation amongst 29 women who all had irregular periods,
- The pheromones from 9 of the women were collected through use of a pad under the armpit, and then rubbed onto the upper lip of the remaining 20 women,
- The researchers found that recipients had shorter cycles when exposed to pheromones from donors in the follicular phase; their own menstrual cycles became shorter by an avg of 1.7 days, with a variability of +/- 0.9 days,
- Researchers found that recipients had longer cycles when exposed to pheromones from donors in the ovulatory phases, their cycles became longer by an avg of 1.4 days, with a variability of +/- 0.5 days.
What is seasonal affective disorder?
- an example of the influence of endogenous pacemakers on the circadian sleep-wake cycle,
- SAD is an infradian disorder caused by disruption to the sleep-wake cycle, and commonly occurs in winter,
- Longer nights means that more melatonin is secreted by the pineal gland, via the endocrine system, leading to feelings of loneliness and depression.
What are the stages of the sleep-cycle?
- Stages 1 and 2 represent the ‘sleep escalator’ where the participant can easily be awoken, stages 3 and 4 coincide with deeper and slower delta waves (compared to theta waves during stages 1 and 2), whilst stage 5 represents REM sleep,
- REM sleep is closely associated with dreaming and characterised by movement inhibition and a sensory blockade.
What did Derment and Kleitman (1957) find?
- Studied 33 adults, where their caffeine and alcohol intake had been controlled, in order to remove the effect of these extraneous variable and increase the reliability of their findings,
- Using EEG scans, the researchers found that discrete periods of rapid eye movement potentials were recorded without exception during each of 126 nights of undisturbed sleep.
- Since participants were able to accurately recall their dreams when awoken from REM sleep, the assumption was made that dreaming is associated with REM sleep,
- This supports the idea of a distinct set of sleep stages.
What did Trevathan et al. (1993) find?
- Noted that he found no evidence of menstrual synchronisation in the all-fenake participants used,
- Suggests that there are external (extraneous) variables which may affect the timing and duration of their menstrual cycles,
- McClintock et al. did not control for such extraneous factors, e.g. exercise, smoking, and alcohol consumption,
- Therefore, this raises doubts about the strength of the influence of pheromones, as an exogenous zeitgeber which can entrain infradian rhythms.
What did Gloth et al. (1999) find?
- That, when treating sufferer of SAD with either Vitamin D supplements or broad-spectrum phototherapy, all subjects receiving vitamin D improved in all outcome measures,
- The phototherapy group showed no significant changes in depression scale measures,
- Patients given vitamin D supplements also experienced a 74% improvement in their depression measures,
- This suggests that phototherapy is ineffective in treating SAD,
- Since phototherapy involves exposure to bright light in order to increase the rate at which the pineal gland secretes melatonin, this implies tthat melatonin and serotonin levels have little parts to play in the development of SAD and in the entrainment of circadian sleep-wake cycles
What did Luo ey al. (2003) find?
- Studied the effects of pheromonal signals in the olfactory bulb of mice,
- Concluded that mammals encode social and reproductive information by integrating vomeronasal ssensory activity specific to sex and genetic makeup,
- Therefore, this suggest that endogenous pacemakers have a critical role in the entraining of biological rhythms in animals.
