Chapter 13_Circadian Rhythms

Question 1

Describe the features of the Earth’s rotation that result in days, years, and seasons.

Answer 1

Day: axial rotation
Year: orbit
Seasons: tilt of axis

Question 2

When discussing biological rhythms in humans, we refer mostly to (daily/yearly/seasonal) variations.

Answer 2

daily

Question 3

True or False? Circadian rhythms depend on sleep/wake times.

Answer 3

False

Question 4

What are some examples of physiological parameters in humans that follow daily rhythms?

Answer 4

Hormones secretion (cortisol, melatonin)
Body temperature

Question 5

What are some examples of psychological parameters in humans that follow daily rhythms?

Answer 5

alertness, rxn time

Question 6

In a typical biological human rhythm, melatonin is (high/low) when alertness is low.

Answer 6

high

Question 7

What is the standard assay used to study rhythms in a lab setting?

Answer 7

running wheel connected to a computer

Question 8

What is a measure used to assess biological rhythms in birds?

Answer 8

perch-hopping

Question 9

What is the name of the output generated from a running wheel when studying rhythms in a lab setting?

Answer 9

actogram

Question 10

Which class of biological rhythms occur more often than once a year but less often than once a day? Name an example of this rhythm.

Answer 10

infradian

e.g. estrus & menstrual cycles

Question 11

What is BRAC? What class of biological rhythms does it belong to?

Answer 11

BRAC = Behavioural Rest and Activity Cycles

ultradian rhythm

Question 12

How often do ultradian rhythms occur?

Answer 12

more than daily

Question 13

What are rhythms that occur on a yearly basis termed?

Answer 13

circannual

Question 14

What is the outcome when humans are placed in time-free environments?

Answer 14

a drift in rhythm (1 hour later each day) – period is >24 hours

Question 15

If the the human circadian clock is running slow (>24 hours), then why do we exhibit 24 hour behaviour/physiology patterns?

Answer 15

response to environmental cycles; “clock” is “re-set” each day

Question 16

What is the advantage of having a clock that doesn’t run at exactly 24 hours?

Answer 16

It permits the clock to track changing dawn/dusk times, as day length changes over the year (except at equator)

Question 17

What is a zeitgeber? What are some examples?

Answer 17

gives info about time and synchronizes circadian clock

e.g. sunrise/sunset, social interaction, exercise, food

Question 18

What is the name of the process through which zeitgebers synchronize the circadian clock?

Answer 18

entrainment

Question 19

What is the most potent zeitberger?

Answer 19

light

Question 20

At what times is light the best cue? What effect does light have at these times?

Answer 20

early morning: nudge ahead

late evening: nudge back

Question 21

The deeper light falls into the night, the (smaller/greater) its effect.

Answer 21

greater

Question 22

The effect of light is maximal around (minimum/maximum) body temperature.

Answer 22

minimum

Question 23

Who was the first scientist to search for the location of the circadian clock?

Answer 23

Curt Richter

Question 24

How did Richter test the idea that activity was the “gear” of the the circadian clock? What were the findings?

Answer 24

He prevented activity for a week. The clock did not stop running, because activity resumed in line with previous pattern.
=> circadian clock is pacemaker

Question 25

If the circadian pacemaker does not drive behaviours directly, what does it control?

Answer 25

It regulates the activity of neural structures that control the behaviours.

Question 26

In Richter's lesioning experiments, a lesion to the __________ disrupted rhythmicity.

Answer 26

anterior hypothalamus

Question 27

Which brain structure is the circadian clock likely localized to?

Answer 27

the suprachiasmatic nucleus (SCN)

Question 28

How is information about the light-dark cycle transmitted to the SCN?

Answer 28

retinal input | the retinohypothalamic pathway

Question 29

How did lesion studies show localization of the circadian pacemaker to the SCN?

Answer 29

when SCN was lesioned, animals became arrhythmic

Question 30

How did metabolic activity localize the circadian pacemaker to the SCN?

Answer 30

Animals were injected with radioactive 2-deoxyglucose. Cells take this up proportionally to their activity. The SCN is the only brain region that takes it up with a rhythm.

Question 31

What is the problem with using a lesioning approach to localize the circadian clock to the SCN?

Answer 31

the SCN could be a connection and not the endpoint of circadian rhythms

Question 32

How did studies of electrical activity show that circadian rhythms may originate from the SCN?

Answer 32

SCN has rhythm of electrical activity when recorded in animal. When isolated in brain, SCN is still rhythmic but other areas are not. When removed from brain, SCN continues to show rhythms in vitro. Single cells within SCN are rhythmic.

Question 33

The clock mechanism in the SCN is (inter/intra)cellular. (How do we know?)

Answer 33

INTRAcellular | Single cells within SCN are rhythmic on their own

Question 34

What is the effect of electrical stimulation of SCN?

Answer 34

phase shifts that match those produced by light

Question 35

True or False? Chemical stimulation of the SCN affects the circadian clock.

Answer 35

True

Question 36

Imagine a scenario where a hamster is in free-running rhythm. A light pulse is provided near the start of its activity period. What occurs?

Answer 36

Phase delay ("nudge ahead")

Question 37

A hamster is in free-running rhythm. A light pulse is provided, and a phase advance is observed. When was the light pulse probably provided?

Answer 37

End of activity cycle

Question 38

What are the lengths of cycles for Tau +/+, +/- and -/- hamsters?

Answer 38

+/+ 24 hrs +/- 22 hrs -/- 20 hrs

Question 39

What happens when a WT SCN is transplanted into a tau mutant hamster?

Answer 39

it adopts a 24 hour cycle

Question 40

Does the SCN exert effects on rhythmicity via neural or diffusible signals? How do we know?

Answer 40

Diffusible signals | Encapsulated SCN grafts sustain rhythmicity

Question 41

Which period gene is associated with delayed sleep phase insomnia in humans?

Answer 41

Period 3

Question 42

What are some circannual cycles controlled by melatonin secretion?

Answer 42

``` gonad size (& sexual behaviour) coat colour ```