Biopsychology: Biological Rhythms (L11-13) Flashcards
1
Q
What are biological rhythms?
A
- cyclical changes in physiological systems
- evolved because the environments in which organisms live have cyclical changes
- e.g. day/night, summer/winter etc
- three types of biological rhythms, circadian, ultradian and infradian
2
Q
What are circadian rhythms?
A
- any cycle that lasts 24 hours
- nearly all organisms possess a biological representation of the 24 hour day
- these optimise an organism’s physiology and behaviour to best meet the varying demands of the
day/night cycle
3
Q
How are circadian rhythms driven?
A
- driven by the suprachiasmatic nuclei (SCN) in the hypothalamus
- this pacemaker (controls the rate at which something occurs)
must constantly be reset so that our bodies are in synchrony with the outside world - natural light provides the input to this system, setting the SCN to the correct time in a process called photoentrainment
- SCN then uses this info to coordinate activity of circadian rhythms throughout the body
4
Q
How does the sleep wake cycle work, CR?
A
- light and darkness are the external signals that determine when we feel the need to sleep and when we wake up
- this rhythm dips and rises at different times of the day
- strongest sleep drives occur between 2:00-4:00am and 1:00-3:00pm
- the release of melatonin from the pineal gland is at its peak during the hours of darkness
- melatonin induces sleep by inhibiting the neural mechanisms that promote wakefulness
- light suppresses the production of melatonin
5
Q
How does homeostatic control affect the sleep wake cycle, CR?
A
- sleep and wakefulness are also under homeostatic control
- when we have been awake for a long time homeostasis tells us that the need for sleep is increasing
- because of the amount of energy used up during wakefulness
- this homeostatic drive for sleep increases gradually throughout the day
- reaching its maximum in the late evening
- circadian rhythms keep us awake as long as there is daylight
- prompting us to sleep as it becomes dark
- the homeostatic system tends to make us sleepier the
longer we have been awake regardless of whether it is night or day - the internal circadian rhythm will maintain a cycle of 24-25 hours, even without natural
light
6
Q
Circadian rhythms, +ve evaluation:
A
- practical application is chronotherapeutics
- the time that patients take medication is very important for treatment success
- is essential that the right concentration of drug is released in the target area of the body at the time the drug is most needed
- like the risk of heart attack is greatest during the early morning hours after waking
- medications have been developed that are taken before the person goes to sleep but are not released until the vulnerable time of 6:00 am
7
Q
Circadian rhythms, -ve evaluation:
A
- research has not isolated people from artificial light as was believed only natural light affected
- more recent research suggests this might not be true
- Cziesler et al. altered participant’s circadian rhythms down to 22 hours and up to 28 hours using artificial light alone
= individual differences in the length of circadian rhythms
= research study found that cycles can vary from 13 to 165 hours - individual difference of when one reaches their peak
- ‘Morning people’ prefer to rise early and go to bed early whereas ‘evening people’ prefer to rise late
= studies of individuals who live in Artic regions, where the sun does not set in the summer months, show normal sleeping patterns despite the prolonged
exposure to light
= suggests occasions where the exogenous zeitgeber of light may have very little bearing on our internal biological rhythms
8
Q
What are ultradian rhythms?
A
- cycles that span a period of less than 24 hours
9
Q
What is the 5 sleep stages, UR?
A
- human sleep follows a pattern alternating between Rapid Eye
Movement (REM) sleep, stage five - and Non-Rapid Eye Movement (NREM) sleep, consists of stages one, two, three and four
- cycle repeats itself every 90 minutes
- each stage shows a distinct EEG pattern
- as person enters deep sleep, their brainwaves slow and their breathing and heart rate decreases
- during the fifth stage (REM sleep), the EEG pattern resembles that of an awake person
- during this stage dreaming occurs
10
Q
What is the BRAC, UR?
A
- Kleitman (1969) referred to the 90 minute cycle found during sleep as the Basic Rest Activity Cycle (BRAC)
- suggested that this 90 minute cycle continues when we are awake
- during the day, rather than moving through the sleep
stages - we move progressively from a state of alertness into a state of
physiological fatigue - studies suggest that the human mind can focus for about 90 minutes
- towards the end of those 90 minutes the body begins to run out of resources
- resulting in loss of concentration, fatigue and hunger
10
Q
Ultradian rhythms +ve evaluation:
A
- Ericsson et al. found support for the ultradian rhythms
- they studied a group of elite violinists
- found that among this group practise sessions were limited to 90 minutes at a time
- violinists frequently napped to recover from practise, with the best violinists napping more
- the same pattern was found among athletics, chess players and writers
- this fits with the BRAC
11
Q
Ultradian rhythms -ve evaluation:
A
- Tucker et al. suggests that there are individual differences in
ultradian rhythms - which are biologically determined and may even be genetic in origin
- participants were studied over 11 consecutive days and nights in a laboratory environment
- researchers assessed sleep duration, time taken to fall asleep and the amount of time in each sleep stage
- they found differences in all of these characteristics
12
Q
What are infradian rhythms?
A
- cycles than span a period of longer than 24 hours
- may last weeks, months or even a year
13
Q
What is the menstrual cycle, IR?
A
- lasts for about a month
- considerable variations in the
length of this cycle - some women experiencing a 23 day cycle and others a 36 day cycle
- average is 28 day.
- hormones regulate the menstrual cycle
- ovulation occurs roughly halfway through the menstrual cycle at day 14
- when oestrogen levels are at their peak, and usually lasts for 16-32 hours
- after ovulation, progesterone levels increase in preparation for the possible implantation of an embryo in the uterus
14
Q
Infradian rhythms, +ve evaluation:
A
- they can affect behaviour
- Penton-Voak found that
women express a preference for feminised male faces when choosing a partner for a long-term relationship - but they showed a preference for masculinised faces during ovulation
15
Q
Infradian rhythms, -ve evaluation:
A
- menstrual cycle is not only governed by infradian rhythms
- when several women of childbearing age live together, and do not take oral contraceptives, their menstrual cycles synchronise
- in one study samples of sweat were collected from one group of women and rubbed onto the upper lip of another group of women
- their menstrual cycles became synchronised
- suggests that the synchronisation is affected by pheromones
- these are a chemical substance produced and released into the environment by an animal which affects the behaviour of others of the same species
16
Q
What are endogenous pacemakers and exogenous zeitgebers?
A
- internal biological rhythms must be finely tuned in order to stay in keeping with the outside world
- to achieve this we have endogenous pacemakers (internal)
- and exogenous zeitgebers (external)
- endogenous pacemakers are body clocks (e.g. the suprachiasmatic nuclei) which regulate biological rhythms
- whereas exogenous zeitgebers are cues (e.g. light) that
entrain our biological rhythms
17
Q
What does the SCN do?
A
- most important endogenous pacemaker is the suprachiasmatic nuclei
- this is a tiny cluster of nerve cells in the hypothalamus
- SCN plays an important role in generating circadian rhythms
- acts as the master clock, linking other brain regions that control sleep and arousal
- and controlling all other biological clocks throughout the body
17
Q
How does the SCN work?
A
- neurons within the SCN synchronise with each other
- so that their target neurons in sites elsewhere in the body receive time-coordinated signals - these peripheral clocks can maintain a circadian rhythm
- but not for very long, which
is why they are controlled by the SCN - is possible because of the SCN’s
built in circadian rhythm - which only needs resetting when external light levels
change - SCN receives information about light levels through the optic
nerve - if our biological clock is running slow then morning light shifts the clock
18
Q
What does SCN do with melatonin?
A
- SCN also regulates the manufacture and secretion of melatonin in the pineal gland
- via the interconnecting neural pathway
- SCN sends a signal to the pineal gland
- directing it to increase production and secretion of the
hormone melatonin at night - and to decrease it as light levels increase in the morning
- melatonin induces sleep by inhibiting the brain mechanisms that promote wakefulness
21
Q
Endogenous pacemakers, evaluation:
A
1+ Folkard (1996) studied a university student, Kate Aldcroft, who spent 25 days in a lab
+ she had no access to the exogenous zeitgebers of light to reset the SCN
+ but at the end of 25 days her core temperature rhythm was still at 24 hours.
+ indicates that we DO NOT need the exogenous zeitgebers of light to maintain our internal biological rhythms
1- Kate Aldcroft’s sleep-wake cycle extended to 30 hours, with periods of sleep as long as 16 hours
- suggests that we DO need the exogenous zeitgebers of light to maintain our internal biological rhythms
22
Q
What are exogenous zeitgebers?
A
- term exogenous refers to anything whose origins are outside of the organism
- exogenous zeitgebers are environmental events that are responsible for maintaining the biological clock of an organism
- most important zeitgebers for most animals is light
23
Q
How does the exogenous zeitgeber of light work?
A
- receptors in the SCN are sensitive to changes in light levels during the day
- then use this information to synchronise the activity of the body’s organs and glands
- light resets the internal biological clock each day, keeping it on a 24-hour cycle
- a protein in the retina of the eye called melanopsin, which is sensitive to natural light, is critical in this system
24
Q
What is the problem with night shift and travelling in regards to EZ?
A
- when people move to a night shift or travel to a country with a different time zone
- their endogenous pacemakers try to impose their inbuilt rhythm of sleep (circadian rhythm)
- but this is now out of synchrony with the exodengeous zeitgeber of light
- out of sync biological rhythms lead to disrupted sleep patterns, increased anxiety and decreased alertness and vigilance
25
Q
Exogenous zeitgebers evaluation:
A
1+ vast majority of blind people who still have light perception have normal
circadian rhythms
+ blind people without light perception show abnormal circadian rhythms
+ shows the vital role that the exogenous zeitgeber of light levels play in maintaining our internal biological rhythms
2+ found that exposure to bright light prior to an east-west flight decreased the time needed to adjust circadian rhythms to local time
1- studies of individuals who live in Arctic regions, where the sun does not set in the summer months, show normal sleeping patterns
- despite the prolonged exposure to light
- suggests that there are occasions where the exogenous zeitgeber of light may have very little bearing on our internal biological rhythms
