Circadian Rhythms

Question 1

Circadian rhythm

Answer 1

• Any cycle that lasts about 24 hours
• A pattern of behaviour that occurs/reoccurs every 24 hours which is reset by environmental light levels
• A good example is the sleep-wake cycle

Question 2

All biological rhythms are regulated and governed by two things

Answer 2

1) Endogenous pacemakers: They body’s internal body clock that regulates biological rhythms e.g detects light
2) Exogenous zeitgebers: External factors in the environment which reset our biological clocks e.g light, social cues

Question 3

Example of circadian rhythm- sleep

Answer 3

• Low levels of light detected by retina
• Message is sent to the CSN via the optic nerve
• SCN stimulates pineal gland to release melatonin which makes us sleepy
• The reverse happens when daylight begins again

Question 4

Animals studies into the SCN- DeCoursey et al (2000)

Answer 4

• They destroyed the SCN connections in the brains of 30 chipmunks who were then returned to their natural habitat and observed for 80 days
• The sleep-wake cycles of the chipmunks disappeared and by the end of the study, a significant proportion of them had been killed by predators (presumably as they were awake and vulnerable to attack when they should have been asleep)

Question 5

Michel Siffre- Cave study

Answer 5

• He tested the internal body clock
• He spent 61 days and nights underground in a cave
• There were no exogenous zeitgebers (lights etc)
• The only influence was endogenous pacemakers
• He settled into a sleep/wake cycle of 25 to 30 hours
• It supports the assumption that endogenous pacemakers exert an influence on circadian rhythms
• It shows the strength of the circadian rhythm as a free-running cycle and questions the extent to which it can be overridden by exogenous zeitgebers