Lesson 10 - Circadian Rhythms Flashcards
What are ‘biological rhythms’?
Cyclical changes in physiological systems
Why did biological rhythms evolve?
Because the environments in which organisms live have cyclical changes
What are the 3 types of biological rhythms?
Circadian, ultradian and infradian
What are circadian rhythms driven by?
Suprachiasmatic nuclei (SCN) in the hypothalamus
What does SCN stand for?
Suprachiasmatic nuclei
Where is the SCN located?
Hypothalamus
What does a pacemaker do?
Controls the rate at which something occurs
Why does the pacemaker have to be constantly reset?
Our bodies are in synchrony with the outside world
What is photoentrainment?
A process by which natural light provides the input to the homeostatic system so that the SCN is set to the correct time
When do the strongest sleep drives occur?
Between 2-4am and 1-3pm
What is at its peak during the hours of darkness?
The release of melatonin from the pineal glands
What does melatonin do?
Induces sleep by inhibiting the neural mechanisms that promote wakefulness
What does light do to melatonin?
Suppresses the production of melatonin
What is sleep and wakefulness under the control of?
Homeostatic control
What happens to the homeostatic drive for sleep throughout the day?
It gradually increases and reaches its maximum at late evening
What is the relation between the homeostatic system and sleepiness?
The homeostatic system makes us sleepier the longer we have been awake, regardless of night or day
What does the internal circadian system maintain?
A cycle of 24-25 hours even without natural light
+ Chronotherapeutics
• Right concentration of drug; released in target area; at time it is most needed
Example:
Risk of heart attack is greatest in the early morning hours after waking
Medications developed that can be taken before sleep; released until vulnerable time of 6:00am
Cziesler et al 1999
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Natural light is not the only thing that can affect circadian rhythms - artificial light can too
Cziesler et al altered participants’ circadian rhythms from 22 and 28 hours using only artificial light
Cziesler et al
1999
Length
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There are individual differences in the length of circadian rhythms
One research study found that cycles can vary from 13 to 165 hours (Cziesler et al)
Morning person
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Individual differences in when circadian rhythms reach their peak
‘Morning people’ rise early, go to bed early
‘Evening people’ rise late
Buhr et al
2010
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Buhr believes temperature controls our body clock, not light
SCN transforms information about light levels -> neural messages -> set body’s temperature
These fluctuations in temperature set the timing of the cells in the body
