L10 - Circadian Rhythms

Question 1

What are biological rhythms?

Answer 1

• Cyclical changes in physiological systems.
• Evolved because env have cyclical changes
• 3 types of biological rhythms: circadian, ultradian and infradian

Question 2

What are circadian rhythms?

Answer 2

• Any cycle that lasts 24 hours.
• Nearly all organisms have a biological representation of a 24 hour day.
• These optimise an organism’s physiology and behaviour to meet the varying demands of the day/night cycle

Question 3

Describe the process of circadian rhythms

Answer 3

• Driven by the Suprachiasmatic nuclei (SCN) in the Hypothalamus
• This pacemaker must constantly be reset so our bodies are in synchrony with outside
• Natural light provides the input, setting the SCN to the correct time in a process called photoentrainment
• The SCN uses this info to coordinate activity in the body

Question 4

What is the Sleep-Wake Cycle?

Answer 4

• Light and dark are external signals that determine when we feel the need to sleep/ wake
• The strongest sleep drives occur between 2-4 am and 1-3 pm
• The release of melatonin from the pineal gland is at its peak when it’s dark. Melatonin induces sleep by inhibiting the neural mechanisms that promote wakefulness
• Sleep is under homeostatic control. Homeostasis tells us when our need for sleep is increasing because energy is used up during wakefulness. This drive increases throughout the day, but is the highest in the evening
• Circadian rhythms keep us awake as long as there is daylight, prompting us to sleep as it becomes dark. The homeostatic system tends to make us sleepier the longer we have been away regardless of light. The internal rhythm will maintain a cycle of 24 hours without natural light

Question 5

Evaluation of Circadian Rhythms (+)

Answer 5

+ Practical application is Chronotherapeutics. The time that patients take medication is important for success of treatment. Medications have been developed that are taken the previous night and are only released at 6 am

Question 6

Evaluation of Circadian Rhythms (-)

Answer 6

• Didn’t take into consideration artificial light. Research shows a circadian rhythm was altered down to 22 hours and up to 28 hours using artificial light.
• Individual differences in length of circadian rhythms. One study found cycles can vary from 13 to 165 hours
• Another individual differences could be peak times. E.g morning people and evening people and their wake time
• Those who live on Artic Regions where the sun does not set in the summer months show normal sleeping patterns. This suggests that exogenous zeitgebers has little bearing on our internal biological rhythms.