biological rhythms Flashcards
endogenous pacemaker
internal mechanism that controls cycles. biological clock
exogenous zeitgebers
external factors that affect our biological rhythms.
originate from outside the individual
circadian rythms
rhythms that last a day (24 hours), daily. examples; the sleep wake cycle, hormone secretion.
infradian rhythms
occur over a period longer than a day.
for instance human menstrual cycle, or birds’ migration patterns (which are annual a.k.a circraanual)
ultradian rhythms
occur in periods of time shorter than 24 hours.
for instance sleep cycles
The sleep wake cycle
- assume around 24 hours asheavily based on day light patterns and other exogenous zeitgebers.
- also can be assumed its dependent on biological endogenous pacemaker
Michael Siffre
-spent 6 months living in Texan caves
-all exogenous zeitgebers were removed, biological clock allowed to roam freely, i.e. eating and sleeping whenever his body demanded (natural inclinations).
-he was wired up and physiological functions such as heart rate monitored.
-at first his sleep-wake cycle was errative but settled in to a 25 hour pattern.
EVAL
-one person case study so sample is very limited.
- living conditions were unnatural, uncontrolled factors such as loneliness may have impacted his circadian rhythms, and ultimately the findings of the study.
SCN’s role in biological rhythms
- small part of the hypothalamus
- responsible for maintenance of circadian rhythms
- lies just above the optic chasm which means it can quickly recieve info from the photoreceptor cells in the retina
- the SCN generates its own rhythms. This impacts the pineal gland that releases the hormone melatonin in low light levels, causing a state of sleepiness.
SCN’s role evidence
- rats with lesioned SCN had their circadian rhythms completely disrupted.
- chickens biological clocks go with dawn break
Human menstrual cycle
- infradian
- goverened by hormones (endogenous biological factor) oestrogen and progesterone work to an endogenous pattern under the control of the pituitary gland.
Human sleep rhythm
- ultradian
- each sleep cycle lasts about 90 minutes
- comprised of a number of stages, repeating on average 5-6 times
- each stage is different in terms of brain activity (viewed on an EEG machine)
- sleep can be divided into REM and non-REM
- Non-REM: first 2 stages are light sleep, 3rd and 4th stages are SWS and are deeper stages of sleep
- stage two is often followed by a periof of REM sleep
Human sleep rhythms evidence
- Biological clocks seem to be the main control mechanism for the stages of sleep
- When the SCN is lesioned squirrel monkeys their sleep cycles and stages were severely disrupted
- Exogenous factors impact sleep- light levels, drugs, temperature
- one study found that alcohol disrupts sleep, However, only one dose of alcohol was used so may not be generalisable to real life/other patterns of alcohol use
Shift work
- disrupts the normal links between the human biological clock and the external zeitgebers people experience.
- meal patterns, social life and minor things like TV viewing are all disrupted
benefits of studying shift work
prevent accidents occurring i.e. circadian trough, a period of time where workers reach peak tiredness between 2am-6am.
different types of shift patterns
-earlies, lates and night shifts- rapid rotating system
HORNE (shift patterns)
- earliers, lates and nights are good as workers often get a period of 24 hours between shifts
- BUT hard for our body to adjust to constantly changing.
- on slower rotating systems it is easier for the bosy to adjust
- it is easier for shift workers to rotate in systems that go forward, this extends the day
Impacts of shift work
- circadian trough
- poor quality sleep and sleep deprivation, build up of sleep debt
- big individual differences in coping with shift work. i.e. the older you are the harder it is
- social disruption
- LONG TERM: suggest shift work is linked with CHD and cancer. Those working shift work had a 3 fold increase of CHD (men) howver, these studies do not always control for job type. demands
lessening the effects of shift work
HORNE suggests:
-moderate amount of caffeine to help with alertness
-short naps no longer than 15 minutes
-brighter light levels
-phase delay: go to bed later get up later, easier than phase adance
CZEISLER , MOORE-EDE, COLEMAN:
-workers on rotating shifts most dislike aspects of work that disregard and disrupt normal bodily rhythms and sleep wake physiology
-schedules that take account of circadian rhythms had the most satisfied workers, with better health
Jet lag
- tiredness and sleep discturbance resulting from disruption of body’s normal biological rhythm
- occurs flying E –> W or vice versa
- HORNE: stress, climate and delays and contribute to the impact of jet lag
impact of jet lag
- day time sleepiness
- fatigue
- impaired alertness
- trouble maintaining sleep
HORNE (larks,owls)
larks deal with jet lag better
Lessening the effects of jet lag
DRUGS
-sleeping pills: HORNE - ineffective, leads to grogginess, possibly worsen jet lag
-melatonin: alleviate jet lag, only likely if taken as dusk/ night due to interactions between melatonin and the biological clock
-SPITZER: jet lagged Norwegian doctors- melatonin had no effect, their medical knowledge may have impacted the findings
-an independent study found melatonin to infact be effective, particularly in east bound travel over 5 hours.
-caffeine: one study found caffeine and melatonin to have a positive impact on jetlag, caffeine particularly for day time sleepiness
DAY LIGHT:
-travellers should go out in day light for first few hours after travel - suppresses the surge of melatonin
ADAPTING:
-as soon as possible adapting to local customs and zeitgebers
Conservation of energy
WEBB
(evolutionary approach) inactivity to conserve energy levels. heart rate and temp decrease
evidence for conservation theory
-small animals have higher metabolic rates and lose heat faster. of WEBB were correct we would also expect these animals to sleep more. ZEPELIN: found a positive correlation between sleep length and metabolic rate. This is limited as there are many factors that can influence sleep not just metabolic rate and body size (not all animals fit in to this pattern)
foraging theory
-animals sleep more if they have a nutrient rich diet as they have to spend less time foraging.
evidence for foraging
pandas eat bamboo which is low in nutrients, they spend up to 16 hours a day eating. animals like cats and dogs who eat nutrient rich food do not eat continuously
food scarcity
sleep should increase when food is scarce. animals have a greater need for conserving energy
evidence for food scarcity
BERGER and PHILLIPS: found this to be correct, sleeping more and decreasing body temp in times of food scarcity
avoidance or predators
prey may sleep more to ensure safety from predators. animals tend to sleep in darkness when most vulnerable
-not the most adaptive, it would seem that a quiet state of alertness would be more effective
evidence for avoidance of predators
ALISON and CICHETTI:
animals slept less in the day if in danger.
39 species, found a negative correlation between amount of sleep and level of environmental danger
However, correlation doesnt always prove causality
Rabits and moles sleep similar amounts of time despite the facts moles are exposed to typically less danger.
restoration theory as evaluation of conservation theory
there is such diversity in species’ sleeping habits, if conservation theory were correct you expect much less variation
restoration theory
rest to restore the body to full psychological and physiological capacity
OSWALD restoration theory
patients recovering from CNS injuries or drug overdose slept more than healthy individuals and had more REM.
suggest the role of REM is for brain repair
-may repair the brain through protein synthesis.
-in particular growth hormones are released in SWS.
This may explain why newborns (who grow quickly) and children sleep more than adults.
HORNE restoration theory
- sleep deprived individuals.
- sleep recovery was concentrated in stage 4 and REM sleep.
- These 2 forms of sleep were critical and ‘core sleep’
- the other stages are ‘optional sleep’
- core sleep is when the body restores and replenishes.
Evidence for restoration theory
-Randy Gardiner case study
-EMPSON: deprived sleepers of REM sleep. on nights where they were allowed REM sleep, REM rate was 50% higher
-MORGANE REM sleep seems to restore neurotransmitters in the brain
HOWEVER other scientists believe this is not true as REM involves neural activity, so we would expect neurotransmitters to be used and not made
Non-REM sleep
stage 1: relaxed, heart rate slows. EEG shows theta waves, slow waves, eyes may role and muscles relax
stage 2: EEG patterns of ‘sleep spindles’ short bursts of high frequency activity
stage 3: delta waves which are large in amplitude and slow. body temp and heart rate slow further
stage 4: delta activity, deep sleep, hard to wake
REM sleep
- REM
- high frequency brain waves
- small amplitude beta waves
- completely relaxed muscles
- heart rate and resps become faster and more erratic
- dreams more likely to be reported
- EEG patterns similar to when awake but all muscles are relaxed everything paralysed except eyes, paradoxical sleep
babies/newborns sleep
Newborns sleep around 18 hours a day in no particular pattern.
50-60% of sleep is REM. May be that REM sleep is important for neurotransmitter restorations and synthesis of the brain-helping the brain to become more organised.
As foetuses we have more REM sleep than at any other point in our life.
children’s sleep
REM sleep decreases with age. At age 2 REM sleep only accounts for around 20-25% of sleep.
At age 5 children have settled into a pattern of around 10-12 hours sleep and rarely take naps.
adults’ sleep
Have around 8 hours sleep per night. However there are big individual differences.
Around the age of 45 REM sleep is about 15-25% of sleep.
Studies have suggested that the purpose of REM is to process the day’s events and new learning. Which may explain why it decreases with age.
sleep in old age
6-7 hours of sleep per night.
Sleep is more fragmented due to a reduction in the amount of deeper stages of sleep.
Some studies suggest that in people over 90 there is no deep sleep.
May be due to melatonin reduction.
REM sleep may be proportionate to young people.
Less REM sleep as learning less.
