Biological Rhythms Flashcards
What are biological rhythms?
Biological rhythms are cyclical changes in the way our biological systems behave. These rhythms have evolved because the environment in which we live has a cyclic changes, e.g day and night
What are the 3 types of rhythms and what do they mean?
Infradian rhythms - A cycle that lasts more than 24 hours e.g. the menstrual cycle.
Circadian rhythm - A cycle that lasts approximately 24 hours, e.g. the sleep-wake cycle.
Ultradian rhythm - A cycle that lasts less than 24 hours e.g the stages of sleep.
Explain the nature of circadian rhythms
There are over 100 circadian rhythms in the human body and are driver by our body clocks. One of the most important examples of a circadian rhythm is the sleep-wake cycle. The fact that we feel drowsy when it’s night-time and alert during the day demonstrates the importance of light as an exogenous zeitgeber (external changes in the environment)
What was the case study done on circadian rhythms?
Siffre’s cave study
-Siffre subjected himself to long periods of time living underground in order to study his own circadian rhythms. -While living underground he had no external cues to guide his rhythms - no daylight, no clocks or radio. He simply woke, ate and slept when he felt it was appropriate to do so.
-After his first underground stay of 61 days (1962) in the cave he resurfaced on September 17th believing it was actually 20th August.
-On his second occasion where he spent 6 months in a cave. His natural circadian rhythm settled down to just over 24 hours, but with some dramatic variations
-On his final underground stay (1999), he was interested in the effects of ageing on circadian rhythms. He found that his body clock ticked more slowly compared to when he was a younger, sometimes stretching his circadian rhythms to 48 hours.
What was another study done to demonstrate that we should not overlook the importance of environmental cues in our internal clock?
Simon Folkard:
Findings - Found that when participants were deprived of sunlight for 3 weeks, and the length of the day was manipulated by the researchers to 22 hours rather than 24, only one ppt easily adjusted to the shortened day
Conclusion - This suggests the strength of the body’s sleep/wake cycle, as it resisted environmental changes
Method - Studies in a group of 12 who agreed to live in a dark cave for 3 weeks. Went to bed when the clock said 11:45 pm and woke when it said 7:45 pm
What are the strengths of the research into circadian rhythms?
-Research into circadian rhythms has practical real world application to shift work - This knowledge has enabled appropriate preventative measures to be put into place e.g changing shifts so that they rotate with, rather than against the clock
-It also has practical real world application to drug treatment. Research into circadian rhythms has revealed that there are certain drugs that are more effective. This has led to the development of guidelines to do with the timing of drug dosing for a whole range of medicines, including anti-cancer, epilepsy and cardiovascular drugs —> Heart attacks are more likely to occur in the morning, so take medication then.
What are the weaknesses of research into circadian rhythms
-Problems with poor control in studies. Even though the ppts in these studies were deprived of natural light and other external cues, they still had access to artificial light. For example, Siffre turned on a dim lamp whenever he was awake as it was believed that it wouldn’t affect the rhythm —> claimed light may act as a confounding variable.
-Problems with the generalisability of case studies - studies of the sleep/wake cycle often involve very small groups or are individual. The people involved are unlikely to be representative of the general population, which makes it’s difficult to generalise findings
—> This generalisability problem is further complicated by the huge amount of individual differences in sleep-wake cycles. Some people generally have different preferences for going to bed early and rising early, whereas some may be the opposite. There are also age differences in the sleep/wake cycle like Siffre proved.
Explain the nature of infradian rhythms
An example of an infradian rhythm is the menstrual cycle.
-The function of the menstrual cycle is to regulate ovulation and this is controlled endogenously by the hormones oestrogen and progesterone
-However, whilst is predominantly controlled internally, evidence does suggest exogenous zeitgebers also play a part too. For example, it is suggested that women’s menstrual cycles can be affected by pheromones of other women (cycles can become synced)
What was the research done by Russell on pheromones?
-Russell gathered sweat samples from the armpits of a donor female by placing cotton pads under their armpits for 24 hours
-The cotton pads were then rubbed on the upper lip of 5 ppts
-This happened 3 times a week for 6 months and at the end of the study, Russell reported that all but one of the ppts had synchronised their menstrual cycle.
Evaluation of Russell’s pheromone study
-This study was a controlled lab experiment and as such seemed to demonstrate clear evidence of the effect of pheromones. However, it is claimed that the clustering of the female menstrual cycle is a myth and no more likely than would be expected by chance alone.
-Furthermore, many of the studies which support this use small samples and rely of women recalling the onset date of menstruation, so this method may be inaccurate.
What is the general evaluation of infradian rhythms?
-There is possible evolutionary explanation for menstrual synchrony. Turke believed there to be an evolutionary explanation for why menstrual synchrony might be an advantage for females to ovulate together and therefore fall pregnant at the same time. This would mean that offspring could be carved for collectively, therefore increasing the chances of survival.
—> However, the validity of this evolutionary explanation has been questioned by Schank who argued that if there were too many females cycling in a social group, this would lead to competition for the highest quality males.
-There are methodological limitation. There are many factors that may effect changes to the menstrual cycle such as stress, changed in diet and exercise. These may act of cofounding variables, suggesting any pattern of synchrony is no more than expected to happen by chance. This could be why others have struggled to replicate findings.
What are the 5 distinct stages of sleep in ultradian rhythms?
-The first 4 stages are called NREM (non-rapid eye movement) and the fifth stage is called REM (rapid eye movement).
-These stages span approximately 90 minutes and so on average there is about 6 sleep cycles per night
What are the key characteristics of sleep stages 1 and 2
Stage 1 - Transition to sleep. Muscles are still quite active and eyes roll
Stage 2- Very light sleep, easily woken, brain waves slow down, heart rate slows and body temp drops
What are the key characteristics of sleep stages 3 and 4?
-Deep sleep. Metabolic rate and heart rate at its slowest
-Slowest brain waves
-Growth hormones produced and the body restores energy and repairs damaged cells.
What are the key characteristics of sleep stage 5?
-Very fast brain activity
-Body is paralysed but eyes more rapidly
-Stage were 75% of dreaming occurs
