Lesson 10 - Circadian Rhythms

Question 1

Biological Rhythms

Answer 1

• Cyclical changes in physiological systems

- Evolved due to environments having cyclical changes - day and night, summer and winter

Question 2

Circadian Rhythms

Answer 2

• Any cycle that lasts 24 hours
• Driven by the suprachiasmatic nuclei (SCN) in the hypothalamus
• This pacemaker must constantly be reset so our bodies are in synchrony with the outside world
• Natural light affects the system, setting the SCN to the correct time in a process called photoentrainment
• SCN then uses this information to coordinate activity of circadian rhythms throughout the body

Question 3

Sleep-Wake Cycle

Answer 3

• Light and darkness are external signals that determine the feeling to sleep/wake
• Rhythm dips and rises at different times in the day
• Strongest sleep occurs between 2-4am and the 1-3pm
• The release of melatonin from the pineal gland is at its peak during hours of darkness - light supresses the production of melatonin
• Sleep and wakefulness are under homeostatic control
• This drive for sleep increases gradually throughout the day, reaching max at late evening
• Internal circadian rhythm will maintain a cycle of 24-25 hours, even without natural light

Question 4

Practical Application - Chronotherapeutics

Answer 4

• The time that patients take medication is very important for treatment success
• Essential that the drug is taken at the time it is most needed
• For example, the risk of heart attack is greatest during early morning hours after waking
• Medications have been developed that are taken before the person goes to sleep but are not released until the vulnerable time of 6am

Question 5

Artificial Light

Answer 5

• Believed artificial light does not affect circadian rhythms
• Cziesler et al 1999 - altered participants circadian rhythms down to 22 hours and up to 28 hours by using artificial light alone

Question 6

Individual Differences - Lengths

Answer 6

• Different people have different length of circadian rhythms
• One research study found that cycles can vary from 13 to 165 hours

Question 7

Individual Differences - Peaks

Answer 7

• Different people have different peaks in their circadian rhythms
• Morning people - prefer to rise early and go to bed early
• Evening people - prefer to to rise late and sleep late