Lesson 10 - Circadian Rhythms

Question 1

What are ‘biological rhythms’?

Answer 1

Cyclical changes in physiological systems

Question 2

Why did biological rhythms evolve?

Answer 2

Because the environments in which organisms live have cyclical changes

Question 3

What are the 3 types of biological rhythms?

Answer 3

Circadian, ultradian and infradian

Question 4

What are circadian rhythms driven by?

Answer 4

Suprachiasmatic nuclei (SCN) in the hypothalamus

Question 5

What does SCN stand for?

Answer 5

Suprachiasmatic nuclei

Question 6

Where is the SCN located?

Answer 6

Hypothalamus

Question 7

What does a pacemaker do?

Answer 7

Controls the rate at which something occurs

Question 8

Why does the pacemaker have to be constantly reset?

Answer 8

Our bodies are in synchrony with the outside world

Question 9

What is photoentrainment?

Answer 9

A process by which natural light provides the input to the homeostatic system so that the SCN is set to the correct time

Question 10

When do the strongest sleep drives occur?

Answer 10

Between 2-4am and 1-3pm

Question 11

What is at its peak during the hours of darkness?

Answer 11

The release of melatonin from the pineal glands

Question 12

What does melatonin do?

Answer 12

Induces sleep by inhibiting the neural mechanisms that promote wakefulness

Question 13

What does light do to melatonin?

Answer 13

Suppresses the production of melatonin

Question 14

What is sleep and wakefulness under the control of?

Answer 14

Homeostatic control

Question 15

What happens to the homeostatic drive for sleep throughout the day?

Answer 15

It gradually increases and reaches its maximum at late evening

Question 16

What is the relation between the homeostatic system and sleepiness?

Answer 16

The homeostatic system makes us sleepier the longer we have been awake, regardless of night or day

Question 17

What does the internal circadian system maintain?

Answer 17

A cycle of 24-25 hours even without natural light

Question 18

+ Chronotherapeutics

Answer 18

• 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

Question 19

Cziesler et al 1999

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Answer 19

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

Question 20

Cziesler et al
1999
Length
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Answer 20

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)

Question 21

Morning person

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Answer 21

Individual differences in when circadian rhythms reach their peak

‘Morning people’ rise early, go to bed early
‘Evening people’ rise late

Question 22

Buhr et al
2010
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Answer 22

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