Exogenous Zeitgebers

Question 1

Social cues

Answer 1

Social conventions entrain biological rhythms such as mealtimes which reset cells in heart and liver highlighting the role of the environment and nurture plays

Question 2

Temperature

Answer 2

Cold temp signals a timer reduced activity
Warm temp is the time for activity. In warm blooded animals, daily changes in body temp are governed by their circadian clock

Question 3

Light

Answer 3

Light is the most dominant zeitgeber and has been found to reset the SCN and other oscillators. This is because a light sensitive protein known as CRY reacts to light and is present in the SCN and throughout peripheral oscillators

Question 4

AO2

Answer 4

Campbell et al found evidence to support that light does act as an exogenous zeitgeber. 15 volunteers slept in a lab and were awoken at separate times with light shone on the backs of their knees. This was found to shift Circadian rhythms highlighting the roles light plays but also how the proteins CRY reacts to light and resets biological rhythms. This also highlights that humans don’t solely rely on light penetrating the eyes and blood may act as a messenger carrying light signals from the skin to the brain.

Boivin et al found that artificial lighting does have an effect on circadian rhythms.

Having a biologically governed system has adaptive advantages but when it goes wrong it can be hard to override. For example, chicurel said familial advanced sleep phase syndrome has been linked to a faulty PER gene causing sleeping and waking up problems and difficulty leading to a normal life.