Circadian Rhythms

Question 1

What are circadian rhythms?

Answer 1

Cyclical patterns within biological systems that repeat roughly every 24 hours (eg. Sleep wake cycle)

Question 2

Endogenous pacemakers

Answer 2

Internal mechanisms that govern biological rhythms (eg. SCN)

Question 3

Exogenous zeitgebers

Answer 3

External mechanisms that govern biological rhythms (eg. Light)

Question 4

Sleep wake cycle

Answer 4

The superchiasmatic nucleus (SCN) in the hypothalamus is stimulated by light penetrating closed eyelids, sending information about day length to the pineal gland. Pineal gland secretes melatonin, inducing sleep

Question 5

Siffre (1972)

Answer 5

Siffre isolated himself in a cave for 6 months devoid of external cues such as light, sound and temperature fluctuations. He found his sleep wake cycle extended to 25 hours but maintained a normal pattern

Question 6

Strengths of circadian rhythms

Answer 6

• Research evidence supporting role of SCN (eg. DeCoursey destroyed SCN connections and found chipmunks sleep wake cycles disappeared and significant number killed by predators)
• Practical application (eg. Boivin found decreased concentration at 6am for shift workers, showing in built body clock out of synch with light. Disrupted rhythms increase anxiety and heart attacks)

Question 7

Limitations of circadian rhythms

Answer 7

• Methodological concerns (eg. Siffre brought artificial light into cave and was the only participant)
• Temperature more important (eg. Buhr found fluctuations in temperature set timing of cells and caused tissues to be active/inactive)