Lesson 11 - Circadian Rhythms

Question 1

What is a circadian rhythm

Answer 1

Cycle which lasts 24 hours

Question 2

What are circadian rhythms driven by

Answer 2

The suprachiasmatic nuclei (SCN) in the hypothalamus

Question 3

What is the input that the SCN uses to reset circadian rhythms

Answer 3

• Natural light

* Process called photoentrainment

Question 4

What are the three circadian rhythms

Answer 4

• Sleep-wake cycle
• Core body temperature
• Hormone production

Question 5

When are the strongest sleep drives

Answer 5

• Between 02:00-04:00

* Between 13:00-15:00

Question 6

How does light/darkness influence sleep

Answer 6

• Release of melatonin from pineal gland is at its peak during dark hours

• Melatonin induces sleep
-inhibits neural mechanisms that promote being awake

• Light suppresses melatonin production

Question 7

What is the other influence sleep and wakefulness is controlled by

Answer 7

• Homeostatic control
• Homeostasis tells bodies that need for sleep increases longer awake for
• Energy used up when awake

Question 8

How do circadian rhythms regulate sleep

Answer 8

Prompts bodies to sleep in dark

-wake when daylight

Question 9

How does the homeostatic system regulate sleep

Answer 9

Makes us sleepier longer we have been awake

-regardless of night or day

Question 10

How long is the internal circadian rhythm

Answer 10

24-25 hours regardless of natural light

Question 11

+ Practical application of studying circadian rhythms

Answer 11

• Chronotherapeutics
• Time patients take meds is important
• Essential that right concentration of drug released in target area at right time of day

Question 12

(-) Research conducted on circadian rhythms lack validity because of this oversight

Answer 12

• Conducted research has not isolated people from artificial light
• Was believed only natural light affected circadian rhythms
• Cziesler et al(1999) altered participant’s circadian rhythms down to 22 hours/up to 28 hours with artificial light
• There may be factors that vary which prevents general conclusions to be drawn

Question 13

• Individual differences in circadian rhythms (1)

Answer 13

• Lengths of circadian rhythms found to vary

• From 13 to 165 hours
-Czeisler et al(1999)

• Suggests circadian rhythms may not be so timely
-understanding is not complete

Question 14

• Individual differences in circadian rhythms (2)

Answer 14

The fact that some people are ‘morning’ and ‘evening’ people implies a difference in the sleep-wakefulness cycle

Question 15

• Studies of individuals in Arctic regions

Answer 15

• The sun doesn’t set in summer
• Normal sleep patterns despite prolonged light exposure
• Suggests exogenous zeitgeber of light may have less bearing on internal biological rhythms than assumed