circadian rhythms Flashcards
(21 cards)
What does ‘circadian’ mean?
The term ‘circadian’ comes from Latin: ‘circa’ means ‘about’ and ‘dian’ means ‘day’ – so it means “about a day.”
What is a circadian rhythm?
It is a biological rhythm lasting about 24 hours, such as the sleep-wake cycle, regulated mainly by light.
What is the sleep-wake cycle?
A circadian rhythm that dictates periods of wakefulness and sleep, primarily regulated by light.
What part of the brain is responsible for regulating circadian rhythms?
The suprachiasmatic nucleus (SCN) in the hypothalamus.
How does the SCN receive information about light?
Light is detected by the eyes and signals are sent to the SCN to help reset the internal body clock.
Apart from circadian rhythm, what other biological process influences the sleep-wake cycle?
Homeostasis – it drives sleep when the body has been awake for a long time due to energy use.
When is the homeostatic drive for sleep strongest?
In the late evening, when most people naturally fall asleep.
When is body temperature at its lowest?
Around 4:30 am (36°C).
When is body temperature at its highest?
Around 6:00 pm (38°C).
How is sleep related to body temperature?
Sleep tends to begin when core temperature drops; rising temperature near morning promotes alertness.
Who was Michel Siffre?
A French cave explorer who studied circadian rhythms in isolation.
What did Siffre do in his study?
He lived underground for months without natural light.
What were Siffre’s findings?
His body clock drifted to a cycle of 25–30 hours, showing that external light cues are crucial for keeping a 24-hour rhythm.
What did Czeisler et al. (1999) find about individual circadian rhythms?
They found that circadian cycles can range from 13 to 65 hours, showing individual differences.
What did Duffy et al. (2001) show regarding chronotype differences?
Some people are morning types (wake/sleep early) and others are evening types, reflecting chronotype differences.
What flaw existed in early studies on circadian rhythms?
Participants were not exposed to natural light but were exposed to artificial light, which was wrongly assumed to have no effect.
How did artificial light affect circadian rhythms in Czeisler et al.’s study?
Dim artificial light shifted circadian rhythms to between 22 and 28 hours, questioning the validity of earlier studies.
What are chronotherapeutics as an application of cricadian rhythms?
The study of how timing of drug treatments affects their effectiveness.
Why is the timing of medication important in circadian terms?
Some conditions (e.g., heart attacks) occur more frequently at specific times, so medication must be timed to maximize benefit.
What is an alternative factor in rhythm regulation other than light?
body temperature
What role does body temperature play in circadian rhythms according to Buhr et al. (2010)?
They argue temperature, not light, is the primary regulator of circadian rhythms, influencing organ and cellular activity.
