Ultradian Rhythms, Endogenous Pacemakers and Exogenous

Zeitgebers

Lesson 3 – Ultradian RhythmsBATs

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?

• List 3 differences between Circadian and Infradian Rhythms

ovulation

LH

FSH

Ho

rmo

ne

Le

vels

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

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 p41. What evidence is there that theBRAC exists?2. Why is the BRAC thought to be important?

Thanks to Eric H Chudler, University of Washington, Seattle USA

The Stages of Sleep

1-4 =

NREM

Stage 1 & 2 – relaxed state, easily woken, heartrate slows, temperature dropsStages 3 & 4 – Slow Wave Sleep (SWS),Metabolic rate slows, growth hormone releasedREM sleep – paradoxical sleep – brain and eyes active, but body paralysed.

Electroencephalograph (EEG) in operation

The stages of sleep as shown on an EEG

Awake

A 1 2 3 4 R C

Stage 1

A 1 2 3 4 R C

Stage 2

A 1 2 3 4 R C

Stage 3

A 1 2 3 4 R C

Stage 4

A 1 2 3 4 R C

REM Sleep

A 1 2 3 4 R C

A 1 2 3 4 R

A

St1

St2

St3

St4

REM REM REM REM

C

These lines represent the EEG (electroencephalogram) 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

MRI scan, showing brain activity during different stages of sleep

StageEEG Rate(Frequency)

EEG Size (Amplitude)

Awake 8-25 Hz Low

1 6-8 Hz Low

24-7 Hz

Occasional "sleep spindles"Occasional "K" complexes

Medium

3 1-3 Hz High

4 Less than 2 Hz High

REM More than 10 Hz Low

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

Lesson 4 – Endogenous pacemakers and Exogenous Zeitgebers

BATsA01 - Define and

compare endogenous pacemakers and exogenous zeitgebers

A02 - Analyse and evaluate evidence of endogenous pacemakers and exogenous zeitgebers

Starter

Endogenous Pacemakers

Internal biological clocksDarlington et al 1998 – clock ‘ticking’ created by

the interactions between certain proteins in the nucleus.

Endogenous Pacemakers

24 hrs

1. CLOCK and CYCLE bind together in the morning

2. Increased production of PER and TIM during the day

3. As PER-TIM levels increase, levels of CLOCK-CYCLE production decrease

4. PER-TIM levels fall CLOCK-CYCLE increases ready to begin the next cycle

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)

Melatonin Secretion

Time of Day

Me

laton

in Le

vel

7 am 7 pm 7 am

asleep

ww

w.p

sych

lotr

on.o

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k

• 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

Endogenous Pacemakers

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!

The Pineal GlandAnother 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

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.

Exogenous Zeitgebers

Exogenous = outside the organism

Zeitgeber = time-giverThe 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).

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).

• 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.

Light as an exogenous zeitgeber

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.

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

Read p 6-7 and do the following tasks

1. 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?

2. Outline evidence that zeitgebers exist.

3. In a table show the advantages and disadvantages of having both endogenous pacemakers and exogenous zeitgebers.

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

Writing essays• 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 Sifrre’s 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

Both endogenous pacemakers and exogenous zeitgebers must be discussed.