sleep is an altered state of awareness
PYA4 – Biological Rhythms,
Sleep and Sleep Disorders
Bio-rhythms
Lessons 1 and 2 : Bio-rhythms
BATs
AO1 - Define and
compare circadian
and infradian
rhythms
A02 - Evaluate the
findings of research
into circadian and
infradian rhythms
Starter
Are you a morning or an
evening person?
Do you find it easier to
get up early or stay
up late?
lark
OR
Bio-rhythms
You may have heard of the term
‘internal body-clock’
What do you think is meant by this?
Discuss in your group examples of events
and bodily functions that seem to follow a
cycle?
http://www.bbc.co.uk/science/humanbody/sleep/crt/ what’s your daily
rhythm? This is on the blog if you want to try this at home
The behaviour of living organisms (plants
and animals) is governed by biological
rhythms.
• Circadian rhythms – 1 day
• Infradian rhythms - > 1 day
• Ultradian rhythms - < 1 day
“ ..the 24 hour circadian rhythm evolved
because the earth revolved”
natural rhythms - the cyclic seasons, the rise and fall of the tides - due to
the orbit of the earth & gravitational pull.
Circadian rhythms
• Latin – ‘Circa’ (about), ‘dies’ (a day)
• Most bodily functions – e.g digestion, body
temperature, heart rate, immune function,
hormone levels show a 24 hour cycle.
• 24 hr ‘sleep-wake’ cycle common to
nearly all animals.
• Regulated by an internal biological
‘clock’ that is readjusted everyday as
environmental time cues change (day
length, seasons).
Some animals sleep all day and are
awake all night!!
Bodily Rhythms
• Endogenous pacemakers
– The internal ‘body clocks’ that generate
biological rhythms
– External factors that regulate or alter
biological rhythms
We will return
to these at a
later date
www.psychlotron.org.uk
• Exogenous zeitgebers
Research into Circadian Rhythms
Watch the video clip and read ‘Cave Man’
and ‘sleep wake cycle’ info on p2 and 3
1. What is meant by ‘free running?’
2. Briefly outline the work of Michel Siffre
(1975)
3. Outline the findings of Aschoff and Wever
(76) and Folkard et al (85)
4. In pairs evaluate the research
Research into Circadian Rhythms
1.
What is meant by ‘free running?’
Biorhythm not affected by external cues, biorhythm governed by internal
(endogenous) ‘clock’
2. Briefly outline the work of Michel Siffre (1975)
Spent time underground in caves, no external cues, woke , ate slept
when he felt like it. Regular circadian rhythm just over 24hrs. At 60
tested the effects of age – internal body-clock slows with age
3. Outline the findings of Aschoff and Wever (76) and Folkard
et al (85)
Aschoff – 22-24hr (some 29hrs) circadian rhythm,
Folkard – most ppts maintained 24 hr rhythm even when clocks were
changed to a 22 hr day
4. In pairs evaluate the research
Artificial light can act as an exogenous zeitgeber Ceizler ’99
Indiv differences range of cycles from 13-65 hrs, ‘larks’ and ‘owls’ can
affect cycle onset
Infradian rhythms
Cycles that have a period greater than
24hrs, but less than a year e.g:
• Menstrual cycle – females
• Male monthly cycle! – body temperature
and mood/alertness
• Seasonal Affective Disorder (SAD) –
also known as a circannual rhythm
The Menstrual Cycle
Hypothalamus
GnRH
Pituitary Gland
FSH & LH
www.psychlotron.org.uk
Ovaries & Uterus
Menstrual cycle
Driven by fluctuating hormone levels. Regulates
ovulation
Pituitary gland in the
brain releases FSH and
LH which stimulate a
follicle in one ovary to
ripen and release an
egg and release the
hormone oestrogen.
FSH = follicle
stimulating
hormone
After 2 weeks, if no
pregnancy, levels
of progesterone
fall and the lining of
the uterus is shed
Once ripe the ruptured
follicle releases
progesterone causing
the uterus lining to
prepare for pregnancy
by increasing blood
supply.
LH = Luteinising
hormone
The Menstrual Cycle
Hormone Levels
FSH
ovulation
www.psychlotron.org.uk
LH
The Menstrual Cycle
• Generated by the hypothalamus
• Fluctuations in hormone levels affect:
– Internal biology (ovulation, menstruation)
– Sexual behaviour (optimal for conception)
– Possible pheromonal mechanism
– Possible evolutionary advantage
www.psychlotron.org.uk
• Apparently influenced by zeitgebers
The Menstrual Cycle
Sexual Activity
Birth control
ovulation
Adams et al (1979)
www.psychlotron.org.uk
No birth control
Can external cues affect the
menstrual cycle?
• Anecdotal (non-scientific) evidence that
menstrual cycles of women living together
for long periods can synchronise.
• Russell, Switz and Thompson (80) –
found when sweat from one woman was
rubbed onto the upper lip of another their
cycles synchronised
• Sweat contains PHEROMONES which
acted as exogenous zeitgebers
Male monthly rhythm
• Empson (1977) - 21 male participants
had body temperature and mood
measured over periods varying from 49102 days.
• Findings showed evidence for periodic
variation in body temp and subjective
ratings of morning alertness.
• Cycle length of approx 20 days
Seasonal Affective Disorder
(SAD)
• A depressive condition which comes on during
the winter months and is gone in the summer.
• Symptoms more severe than the normal
lowering of mood when daylight hours are
shorter.
• Research shows that the hormone melatonin
is secreted when it is dark. The more
darkness the more melatonin.
• Melatonin (secreted by the pineal gland in the
brain) is related to chronic depression.
Summarising Infradian Rhythms
• Read about Infradian Rhythms on p4 and
5 of the Complete Companion
• Answer questions 3 and 4 on p5 – you
could use the same headings as in the
book to help you
Plenary
• Fill in the blanks on the sheet about
Circadian Rhythms
A Circadian Rhythm: The Sleep–Wake Cycle
Copy and fill in the blanks.
A circadian rhythm repeats in a cycle of once every 24
hours. Mammals possess about 100 circadian
rhythms. The 24-hour sleep–wake cycle is a good
example of a circadian rhythm because it clearly
illustrates that circadian rhythms depend on an
interaction of physical and psychological processes.
The fact that we maintain a fairly consistent sleep
pattern suggests an internal mechanism, the biological
clock. However, this can be overridden by
psychological factors, e.g., anxiety can disrupt the
sleep pattern.
When the internal clock is free of external cues, e.g.
clocks, daylight and social cues it is said to be ‘freeRunning’.
Applying Knowledge
• Read about Core body temperature and
Hormones on p 2 and 3
• Add notes to the sheet you filled in about
the sleep-wake cycle
• Choose to find out more about …..
• Chronotherapeutics see p3
• Or Phototherapy to treat SAD see p5
We will share what you
find out in 35 mins
Homework
In next week
please
• Learn the definitions of each type of biorhythm and key words.
• Are explanations of biological rhythms
deterministic? To what extent is this a
good or a bad thing? (see p5 Complete
Companion) – 8 marks AO2/3
• Research methods worksheet or complete
collecting data for experiment ready for
next week