biopsych part 2 Flashcards
what is a biological rhythm
Periodic biological fluctuations in an organism that corresponds to, and is in response to, periodic environmental change
what are the three types of biological rhythm
circadian, infradian and ultradian
what is a circadian rhythm
A type of biological rhythm which completes one full cycle every 24 hours e.g. the sleep-wake cycle. Like other biological rhythms, it is affected by both endogenous pacemakers and exogenous zeitgebers
what are examples of circadian rhythms
sleep wake cycle
body temperature
hormone production (cortisol and melatonin)
what is the sleep wake cycle
within a 24-hour period, we have one period of wakefulness and one period of sleep. This is controlled by our suprachiasmatic nucleus (SCN), which has its own cycle but can be affected by light
what is the body temperature cycle
we cycle between our lowest temperature (36°) at 4.30am and highest (38°) at 6pm. Our body temp. lowers as our body prepares for sleep
what is the hormone production cycle
melatonin makes us sleepy and is at its highest at midnight and lowest at 6am. Cortisol keeps us alert and is on an opposite cycle (highest at 6am, lowest at midnight)
strengths of circadian rhythms
- Siffre – lived in a cave, away from time cues, for several months. Found that even without light, social cues etc. he still kept to a fairly routine daily cycle (25 hours, tho it did differ to as high as 48hours). Demonstrates the existence of a natural circadian rhythm.
- Real world application – knowledge of these circadian rhythms can help, for example with medicine (chronotherapeutics). For example, heart attacks are more common in the morning, so prevention medicine should be taken at night as sleep must involve regulatory functions
limitations of circadian rhythms
- Extraneous variables – a problem with research such as Siffre’s cave study is the impossibility of ruling out time cues. For example, he used artificial lighting. Czeisler was able to entrain participant rhythms from 22-28 hours using artificial lighting.
- Individual differences – not everyone’s circadian rhythms are the same. Czeisler found cycle length varied from 13-65 hours across people. Also, some people nap or have a siesta – so their sleep/wake cycle is not the same as everyone else.
what is an infradian rhythm
with a frequency of one complete cycle occurring less than once every 24 hours. Such rhythms are entrained by endogenous pacemakers and exogenous zeitgebers
examples of infradian rhythms
menstrual cycle and SAD (seasonal affective disorder).
what is the menstrual cycle
lasts roughly 28 days, though cycle lengths vary from person to person (and for many
people, from month to month). During each cycle, rising levels of the hormone oestrogen cause the ovary to develop an egg and release it (this is known as ovulation). After ovulation, the hormone progesterone helps the womb lining to grow thicker, readying the womb for pregnancy. If pregnancy does not occur, the womb lining leaves the body as menstrual flow.
what is seasonal affective disorder
Depressive condition common in winter months, brought about by lack of sunlight causing an excessive amount of melatonin (causing fatigue)
strengths of infradian rhythms - menstrual cycle
Cycle may be controlled externally rather than only by these hormones – McClintock effect (menstrual cycles of women synchronised to a donor if exposed to sweat from the donor). Other factors can also affect it, such as diet and stress.
limitations of infradian rhythms - menstrual cycle
However, the McClintock Effect could be explained through inconsistent cycles. Eventually two cycles of differing lengths will synchronise anyway.
strengths of infradian - seasonal affective disorder
Phototherapy (exposure to bright light) is a more effective treatment for symptoms of SAD than placebo (Miller)
limitations of infradian - seasonal affective disorder
Could be other seasonal factors, such as social support. People tend to spend more time indoors during the winter, so SAD could be explained by social isolation rather than melatonin.
what is an ultradian rhythm
with a frequency of one complete cycle occurring more than once every 24 hours
what is an example of ultradian rhythm
stages of sleep, where a full sleep cycle takes 90 minutes to complete
what is the sleep stages
During sleep we experience 5 stages of sleep, in 90-min cycles (see diagram).
Stages 1 & 2 – light sleep
Stages 3 & 4 – deep, Slow-Wave Sleep (SWS). This is where protein synthesis happens, helping the body to recover.
REM stage – dream sleep. The brain is very active and EEG waves look similar to a waking brain.
what is the brac
Basic Rest Activity Cycle - Just as with sleep stages, we have 90 minute cycles of alertness and fatigue throughout the day
(see diagram).
strengths for sleep stages
Dement & Kleitman woke people during REM or Non-REM (stages 1-4). 89% woken during REM recalled dreaming. Only 7% recalled dreams if woken during NREM.
limitations for sleep stages
Sleep cycle varies throughout your life. 50% of REM and 50% SWS as an infant; in old age, you have very little of either and mostly stages 1 & 2.
strengths for brac
- Ericsson – observed high-performing individuals (e.g. violinists) and noticed consistent 90-min cycle patterns, with the best performers the ones who napped most frequently
- Explains and helps to create workplace and school schedule (roughly 90-120 minutes between breaks)
what is an endogenous pacemaker
internal cues to regulate rhythms
example of endogenous pacemakers
Includes Suprachiasmatic nucleus (SCN) – Found in the hypothalamus. This has its own protein life cycle that lasts 24 hours, which helps to dictate the organism’s circadian rhythms.
what are exogenous zeitgebers
external cues to regulate rhythms
what are examples of exogenous zeitgebers
Light – is received by the photoreceptors in the retina, which inhibits melatonin levels to keep us alert Social cues – other people’s actions affect our rhythms (e.g. noise in the house; alarm clock to make it to school on time)
strengths of eps and ezs
- Morgan – bred hamsters with 20 hour rhythms and implanted their SCN in newborns, who adopted 20-hour rhythms. Shows power of the SCN.
- Siffre – spent 6 months in a cave away from all exogenous zeitgebers. Still kept to a regular 25 hour rhythm, despite having no exogenous zeitgebers.
limitations of eps and ezs
- Czeisler - Artificial light was able to entrain participants’ circadian rhythms from 22-28 hours. This shows the power of artificial light to override the SCN.
- Siffre – the fact that he kept a 25-hr rhythm suggests that we need exogenous zeitgebers to keep us in line with the world’s 24-hour clock.
