Synchornization + Photic Rhythms

Question 1

When is ZT/CT0 and ZT/CT12?
Zeitbeger Time (ZT)
Circadian Time (CT)

Answer 1

ZT0 - Sunrise
ZT12 - Sunset

CT0 - Start of day/activity
CT12 - End of day/sleep

Question 2

tau - Zeitgeber (T) = Phase shift

Answer 2

tau = Period of endogenous rhythm in constant conditions

T = Length of Zeitgeber cycle

Phase shift = Rapid change in an oscillation from one phase to another

Question 3

Resonator vs Oscillator

Answer 3

Oscillations produced at natural resonance frequencies (passive oscillations)

System produces an oscillation using energy (active oscillations)

Question 4

Clock
(3)

Answer 4

Oscillator that has:
1) A frequency matching the Zeitgeber
2) A phase set by the rhythm being followed
3) An output phase that is readable

Question 5

Entrainment
Freerunning

Answer 5

When an organism responds to an internal clock and syncs to the cycle they’re measuring

When the period will keep shifting

Question 6

2 ways that entrainment can occur
Which one does nature use?

Answer 6

Change the period

Reset the phase everyday
- What nature uses

Question 7

Aschoff’s Rules
(Entrainment)

Answer 7

Increasing light intensity
- Tau increases in nocturnal animals
- Tau decreases in diurnal animals

• Alpha (length of daily activity) decreases in nocturnal animals
• Increases in diurnal animals
• Nocturnal animals -> tau < 24 hours
• Dirunal -> tau > 24 hours

Question 8

Why is the endogenous circadian period not 24 hours exactly? (5)

Answer 8

• Expensive to be precise
• Bot necessary to be precise
• Small misalignments may exist for long periods of time
• Phase angle would need to be adjusted to changes in the enviro
• Adjusting would still be required even w/ precise clock

Question 9

Properties of a clock

Answer 9

Freerunning period is close to but not equal to zeitgeber cycle and is under constant conditions

Settable to cyclic enviro

Endogenous (generated by organism)

Innate (genetically determined)

Period is compensated for temperature changes (Q10 = 1)

Question 10

Light in the morning/late night causes phase ___
Light in the evening/early night causes phase ___

Answer 10

Advances (earlier in the day)
Delays (later in the day)

Question 11

If the freerunning rhythms in different organisms can be different from one another, even longer and shorter than 24 hours, then how does the same pulse of light produce entrainment?

Answer 11

The same light may produce delays or advances of appropriate size, depending in when (what phase) in the cycle the light falls.
(Relationship represented by phase response curve)

Question 12

Non parametric entrainment
Parametric entrainment

Answer 12

Entrainment based solely on presence/absence of light
- Accomplished they daily phase shifts
- Ex: Entrainment to bright sunlight

Entrainment that involves qualities of light such as intensity, duration, wavelength
- Ex: Entrainment to sunrise or subset (intensity and wavelength are changing)

Question 13

Intensity-Duration reprocity

Answer 13

Phase shift is the same for a short/bright pulse as a long/dim pulse of light
- Overall energy (photons) is the same

Question 14

Dead zone
Forbidden zone
(Phase response curve)

Answer 14

No shift happening

Stable entrainment not possible
- Phase shifts don’t compensate for difference between T and tau