Types of Biological Rhythms Flashcards
All living things are subjected to biological rhythms that influence the way the body systems work. All biological rhythms are governed by two things:
- the body’s internal biological clocks (endogenous pacemakers)
- external changes in the environment (exogenous zeitgebers)
What are the three rhythms:
- circadian
- infradian
- ultradian
Circadian rhythm:
- repeats approximately once every 24 hrs, e.g. sleep/wake
- Driven by our body clocks and is found in all of the cells of our body
- All of it is synchronised and the master circadian pacemaker, the suprachiasmatic nucleus (SCN) is found in the hypothalamus
- This pacemaker must constantly be reset by external input so that our bodies are in synhrony with the outside world.
What is the master circadian pacemaker?
the suprachiasmatic nucleus (SCN) - found in the hypothalamus
+must constantly be reset by external input so that our bodies are in synhrony with the outside world
Examples of circadian rhythms:
- sleep/wake cycle
- core body temperature
Sleep/wake cycle:
- light/darkness are the external signals (exogenous zeitgebers) that determine when we feel the need to sleep/wake
- SCN responds to increases in light by triggering the depletion of melatonin which leads to us being awake
- When it’s dark, increase in melatonin-> sleep
- Also, when we have been awake for a long period - homeostasis leads to need for sleep increasing as energy is being used up by wakefulness
- Drive for sleep gradually increases throughout the day, reaching maximum in late evening as energy depletes-> fall asleep
Core body temperature:
- Body temp tends to be at its lowest at about 4:30 am (approx 36C) and its highest around 6pm (approx 38C)
- Lower temp makes us feel more sleepy than usual
Infradian rhythms:
- Repeat less than once every 24hrs (longer than a day), e.g. menstrual cycle
- The menstrual cycle is regulated by hormones (endogenous pacemakers)
- Rise of oestrogen leads to ovulation (release of an egg from ovaries) coordinated by the pituitary gland - usually lasts 16-32 hours (oestrogen levels at peak)
- Hormones also stimulate uterus for fertilisation and lead to menstruation
- On average, the cycle lasts around 28 days
Research into / eval of infradian rhythms:
- Russel et al collected samples of sweat from a group of women and applied it to the upper lip of a second group of women;.
- Even though the women kept separate, they found that the menstrual cycle of women in the second group synchronised with the woman who was the odour donor.
- Shows that our understanding of IR being influenced and regulated by biological chemicals like pheromones is accurate - proven by women who’s cycles ‘shift’ when exposed to biological chemicals - can infer that IR is biologically determined.
Criticism of this research / eval of infradian rhythms:
- Critics of this research have argued that many factors may influence the menstrual cycle- diet, stress, exercise - these factors act as extraneous variables and question the C+E between pheromones and menstrual cycle.
- Furthermore, research used small samples of women which is not generalisable to the wider public and relied on self-report of onset of cycles and such recollection might not be accurate
- Trevarthen et al failed to find evidence of menstrual synchrony - thus weakens the supporting evidence and undermines our understanding of IR
Ultradian rhythms:
- Repeats more than once in 24 hours
E.g. sleep cycle involves stages of sleep -Cycle of REM / NREM sleep over time - In one night, there is approximately 5 sleep cycles which last for approximately 90 mins each
Research into ultradian rhythms:
- In NREM sleep - four stages - which progress from shallow (stages 1 and 2) into deep or slow-wave sleep (SWS stages 3+4)
- When individuals fall asleep, they start in stage 1 - moving to 2, descending to the deeper levels of stage 3 and 4 sleep
- The sleeper then starts to climb back through the stages 3 and 2 and this is then followed by REM sleep.
- After a period of REM sleep, which ends the 90 minute cycle, the sleeper descends into the deeper stages of 3 and 4 again
- This is known as the sleep staircase and occurs 5 times a night
Circadian evals:
- A strength of research into circadian rhythms is that there is research support for the role of light as an external pacemaker
- evidence that individual differences are biologically determined
A strength of research into circadian rhythms is that there is research support for the role of light as an external pacemaker.
Hughes tested hormone release in 4 ppts at an Antarctic station + found in Feb (summer) cortisol levels were highest when ppt waking up and lowest when about to go sleep. After 3 months of darkness + changes in daylight patterns - cortisol release patterns peaked in afternoon instead. Shows the role of light in circadian rhythms as it demonstrates that changes in daylight cycle cause changes in our circadian rhythms and the hormone release cycle.
Adds validity to our understanding of circadian rhythms and its causes.
A strength of research into circadian rhythms is that there is evidence that individual differences are biologically determined
Tucker et al: studied ppts over 11 consecutive days and nights in a strictly controlled lab env. Researcher assessed sleep duration, time to fall asleep and amount of time in each sleep stage + found large individual differences in characteristics such as sleep duration and time to fall asleep remained consistent over this time. Shows that changes in sleep conditions did not lead to changes in sleep patterns - seems that sleep habits r biologically determined rather than driven by external factors. Validating our understanding of circadian rhythms
