Ultradian Rhythms, Endogenous Pacemakers and Exogenous Zeitgebers

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Ultradian Rhythms, Endogenous Pacemakers and
Exogenous Zeitgebers
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Lesson 3 Ultradian Rhythms

• BATs
• A01 -Define REM and NREM sleep and the BRAC
• Describe the different stages of sleep
• A02 - Analyse evidence related to BRAC and the
  stages of sleep

• Starter
• What does REM stand for?

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• List 3 differences between Circadian and
  Infradian Rhythms

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Ultradian Rhythms

• The sleep-wake cycle takes one
• day (circadian)
• Whilst asleep another rhythm exists ULTRADIAN
  (less than a day)
• Lasts for 90 minutes
• Involves 2 types of sleep NREM and REM sleep
  within the 90 min cycle.
• Repeats several times throughout sleeping period

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Basic Rest-Activity Cycle

• The 90 minute clock seems to be ticking when
  asleep and throughout the rest of one day.
• Known as Basic Rest-Activity Cycle
• (BRAC)
• Read about BRAC on p4
• What evidence is there that the
• BRAC exists?
• 2. Why is the BRAC thought to be
• important?

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The Stages of Sleep
Thanks to Eric H Chudler, University of
Washington, Seattle USA
1-4 NREM
Stage 1 2 relaxed state, easily woken,
heart rate slows, temperature drops Stages 3 4
Slow Wave Sleep (SWS), Metabolic rate slows,
growth hormone released REM sleep paradoxical
sleep brain and eyes active, but body
paralysed.
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The stages of sleep as shown on an EEG
Electroencephalograph (EEG) in operation
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Awake
A
1
2
3
4
R
C
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Stage 1
A
1
2
3
4
R
C
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Stage 2
A
1
2
3
4
R
C
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Stage 3
A
1
2
3
4
R
C
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Stage 4
A
1
2
3
4
R
C
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REM Sleep
A
1
2
3
4
R
C
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A
St1
St2
St3
St4
A
1
2
3
4
R
C
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These lines represent the EEG (electroencephalogra
m) which shows a record of brain activity the
EMG (electromyogram) shows muscle activity the
EOG (electroculogram) shows eye movements. Look
at the differences in the EEG, EMG and EOG during
waking, REM sleep (Rapid Eye Movement Sleep) and
NREM sleep
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MRI scan, showing brain activity during different
stages of sleep
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Stage EEG Rate(Frequency) EEG Size (Amplitude)
Awake 8-25 Hz Low
1 6-8 Hz Low
2 4-7 HzOccasional "sleep spindles"Occasional "K" complexes Medium
3 1-3 Hz High
4 Less than 2 Hz High
REM More than 10 Hz Low
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Plenary

• Match the number cards to the stage of sleep it
  represents.

Stage type State of body Brain waves
1 2 NREM relaxed state, easily woken, heart rate slows, temperature drops Medium frequency Low - medium amplitude
3 4 NREM Slow Wave Sleep (SWS), Metabolic rate slows, growth hormone released Low frequency High amplitude
REM brain and eyes active, but body paralysed. Higher frequency Low amplitude
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Lesson 4 Endogenous pacemakers and Exogenous
Zeitgebers

• BATs
• A01 - Define and compare endogenous pacemakers
  and exogenous zeitgebers
• A02 - Analyse and evaluate evidence of endogenous
  pacemakers and exogenous zeitgebers

• Starter

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Endogenous Pacemakers

• Internal biological clocks
• Darlington et al 1998 clock ticking created
  by the interactions between certain proteins in
  the nucleus.

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Endogenous Pacemakers
1. CLOCK and CYCLE bind together in the morning
24 hrs
4. PER-TIM levels fall CLOCK-CYCLE
increases ready to begin the next cycle
2. Increased production of PER and TIM during the
day
3. As PER-TIM levels increase, levels of
CLOCK-CYCLE production decrease
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The Suprachiasmatic Nucleus (SCN)

• In mammals, the main endogenous pacemaker is a
  pair of tiny clusters of nerve cells called the
  SCN, which lie in the hypothalamus, just above
  the optic chiasm (where the optic nerves from
  each eye cross over)

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Melatonin Secretion
asleep

Melatonin Level


www.psychlotron.org.uk
7 am 7 pm 7 am

Time of Day
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Endogenous Pacemakers

• Even when our eyes are shut the SCN gets info on
  light from the optic nerve. Light can penetrate
  the eyelids and special photoreceptors in the eye
  transfer light signals to the SCN.
• If our endogenous clock is running slow the
  morning light automatically shifts the clock
  ahead so it is in synchrony with the world
  outside
• See Psyonline PYA4

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Campbell and Murphy (1998)

• Found that when light was shone on the back of
  participants knees many were able to shift the
  circadian rhythms of body temperature and
  melatonin secretion, suggesting that light can
  reach the brain without passing through the eyes!

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The Pineal Gland

• Another endogenous pacemaker that works with the
  SCN is the Pineal Gland.
• Contains light sensitive cells.
• When light is sensed melatonin production is
  inhibited.
• When light level falls melatonin production
  increases
• This induces sleep by inhibiting brain mechanisms
  that promote the awake state.

Light, the pineal gland and melatonin regulate
the sleep-wake cycle
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Read p 64-65 and do the following tasks

1. Why is the pineal gland especially important in
   birds and reptiles?
2. Copy a diagram of the biological clock idea put
   forward by Darlington et al in 1998
3. Bullet point sources of evidence that endogenous
   pacemakers exist.

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Exogenous Zeitgebers

• Exogenous outside the organism
• Zeitgeber time-giver
• The biological-clock is reset each day by cues in
  the environment like the light cues of sunrise
  and sunset.
• This process is called entrainment, (the opposite
  of free-running where the biological clock works
  free of any exogenous cues, including social cues
  like clocks).

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Which are more important exogenous zeitgebers
social cues or light?

• Until recently biologists believed that daily
  rhythms were entrained by social convention (set
  meal and bedtimes), not internal biology.
• Since the discovery that exposure to bright light
  suppresses melatonin production it is now
  recognized that light is the dominant zeitgeber
  in humans (Wever et al 1983).

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Light as an exogenous zeitgeber

• Daylight resets the biological-clock, but dim
  light is less effective.
• Hall (2000), found that proteins called
  cryptochromes found throughout the body can
  detect changes in light.

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What if you are blind?

• Lack of info about light messes up sleep
  patterns.
• Miles et al (1977) young man, blind from birth
  had a circadian rhythm of 29.4 hours. Even with
  the help of clocks and social cues he was unable
  to reduce the pace of his biological rhythm.
• He had to take stimulants in the morning and
  sedatives at night.

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Temperature as a zeitgeber

• Bio-rhythms can also be entrained by temperature
• Leaves fall from deciduous trees in autumn
  because of changes in temperature as well as day
  length.
• A factor in the onset of hibernation.
• No evidence that it affects human bio-rhythms

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Read p 6-7 and do the following tasks

• How could the discovery of cryptochromes give
  support to the study by Campbell and Murphy
  (1998) and explain why some blind people have
  normal bio-rhythms?
• Outline evidence that zeitgebers exist.
• 3. In a table show the advantages and
  disadvantages of having both endogenous
  pacemakers and exogenous zeitgebers.

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Writing essays

• Discuss the role of endogenous pacemakers and
  exogenous zeitgebers in biological rhythms. (25
  marks)

• AO1 general but accurate description of the
  role of endogenous pacemakers and exogenous
  zeitgebers in bio-rhythms.
• Describe the brain mechanisms underlying
  endogenous pacemakers and/or the interaction with
  zeitgebers e.g. light
• base answers on studies e.g. isolation (Siffre),
  role of pheromones and menstrual cycle, Morgan
  (95) hamsters expt - suprachiasmatic nucleus

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Writing essays
Both endogenous pacemakers and exogenous
zeitgebers must be discussed.

• Discuss the role of endogenous pacemakers and
  exogenous zeitgebers in biological rhythms. (25
  marks)

• AO2 Do not just describe the studies.
• - Use them e.g the implications of Sifrres
  work.
• How relevant are the studies to the role of
  endogenous pacemakers and exogenous zeitgebers
• How has the use of electric lighting in the last
  100 years affected biological rhythms
• Issues and debates use of non-human animals
  e.t.c