Endogenous Pacemakers

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  • Created by: hrweaver
  • Created on: 30-12-13 20:12

Endogenous Pacemakers

Endogenous Pacemakers

Also known as the SCN (superchiasmatic nucleus)

Located in the hypatholamus in mammels

Obtains information via the optic nerve about light

Ventral SCN is easy to reset; Dorsal SCN is hard to reset

Pineal Gland and Melatonin

SCN sends signals to the pineal gland telling it to produce more melatonin at night

A02- Morgans mutant hamsters

He genetically built hamsters with the circadian rhythm of 20 hours

He then transplanted the SNC of the mutated hamsters in to 'normal' hamsters. They displayed the 20 hour rhythm proving the role of the SCN.

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Exogenous Zeitgebers

Exogenous Zeitgebers

Entrainment- Resetting the biological clock

Light- The dominant zeitgeber-Can reset the pacemaker-can reset the protein clock.

Campbell and Murphy- If you shine a light on the back of someones knees the circadian rhythm shifts.

Social Cues e.g mealtimes, bedtimes

Social cues also appear to entain circadian rhythms, not just internal biological methods

Zeitgeber for cells, liver and heart is mealtimes as they are reset by eating. (Davidson 2006)


Leaves of diciduous trees change colour due to temperature and day length


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Exogenous Zeitgebers A02


Boivin supports that circadian rhythms can be entrained by dim light

Our society lives in artificial lighting. Stevens suggested that this disrupts biological rhythms and therefore this is why women in well lit, industrialised societies suffer from breast cancer more.

Sleep phase disorders makes people have unusual sleep patterns

Exogenous and Endogeous aren't a clean cut division they both work together

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Ultradian Rhythms- Sleep stages

Sleep follows circadian rhythms however within sleep there is another type of rhythm called an ultradian rhythm- (A rhythm less than a day)

5 sleep stages; first 4 NREM and 5th is REM sleep

One sleep cycle lasts 90mins

Awake stage produces beta waves. Amplitude of waves increase as you go through sleep.

Stages 1 and 2; alpha and theta waves. Relaxation. Low heart rate. Temperature drops

Stages 3 and 4 Delta Waves, low metabolic rate. Growth hormone produced

REM sleep 'paradoxical sleep'. Brain and eyes active, body paralysed. Hard to awaken someone

Goes 1, 2, 3, 4, 3, 2, REM, 2, 3, 4, 3, 2, REM


Assumption that REM sleep is dreaming Demet and kleitman demonstrated this link by waking participants up in REM sleep. They reported dreaming.

They also found that dreams were recorded outside of REM sleep

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