Test 3 Flashcards
Draw the phase advances and delays that occur at 12pm (noon), 6pm, 9pm, 4am, and 6am (dusk). Label them as A, B, C, D, E and indicate where midnight is on the PRC along with if there is a phase advance or delay at midnight
See Slides
There is no phase advance or delay at midnight
Explain how light entrains both diurnal and nocturnal animals to the 24-hour day/night cycle
Responsiveness to light is confined to subjective night in both diurnal and nocturnal species.
When normally exposed to light, during mid-subjective day for diurnal animals, light has no effect on the circadian system.
When not normally exposed to light, during CT 18 or mid subjective night for both diurnal and nocturnal animals, no response to light occurs.
However, when the sun rises in the morning, during subjective day, a phase advance is produced and diurnal animals begin activity earlier.
Light falling at dusk, or late subjective day, produces a phase delay so the activity is continued longer.
An animal, kept in constant dark in the lab, whose free-running sleep-wake cycle is 25 hours long and who is given a pulse of light at circadian time 6 and 15. Would it now demonstrate a sleep-wake cycle that was advanced or delayed and by how many hours? Make it clear as to how you arrived at your answer
CT 6 = 0 hour delay or advance
CT 15 = 3 hour delay
CT 6 + CT 15 = 3 hour delay
List 4 points on the graph that you drew that have no functional significance for animals in their natural habitat
A: mid-subjective day, no effect of light
C: subjective night, dark, no light in natural habitat
D: subjective night, dark, no light in natural habitat
CT 18: mid-subjective night, no light, no light in natural habitat, even if given light –> no effect
Explain the functional effect on the sleep-wake cycle if an individual was kept in constant dark and was given a light pulse at CT 12.
1 hour phase delay
Define Zeitgeber and name the most common Zeitgeber that is used by both plants and animals
Literally time giver. The environmental cue that synchronizes the endogenous circadian rhythm with the environment. Light is the most common Zeitgeber.
Define entrainment
The daily resetting of the clock by some external cue such as light so that rhythms are synchronized or entrained to the 24 hour exogenous cue
Define free running rhythm
Rhythm that is not entrained to an external cue but is running on its own internal period.
Define phase advance
A rhythm that is starting earlier than previously
Define phase delay
A rhythm that is starting later than previously
List 7 ways in which larks and owls are different behaviorally
Bedtime: Larks 11:30 +/- 1hr (can be very late for extreme larks) Owls 1 am +/- 1 hr (can be very early for extreme owls)
Wake Up: Larks 7 am +/- 1hr Owls 8 am +/- 1hr
Ease of Sleep: Larks easy Owls hard
Mood in AM: Larks good Owls bad
Variation in Bedtime: Larks little Owls highly variable
Naps: Larks brief/rare Owls longer/frequent
Awake all Night: Larks very rare Owls more frequent
Sleep Quality: Larks good but inflexible Owls poor but flexible
List 5 reasons why larks and owls are different
- Body temperature and rest activity cycle are synchronized in different phase relationships
- Owls have longer body temperature rhythm than larks
- Owls are less sensitive to the entraining Zeitgeber
- SCN pacemaker not as strongly modulated by neural inputs that affect body temperature in owls as it is in larks
- Larks and owls have different clock genes
List and explain 4 reasons why some people become jet-lagged after crossing several time zones
- Fatigue or sleep loss directly linked to travel and independent of timing conflict
- Differences in external and internal body time.
- Clocks controlling the sleep-wake cycle and body temperature resynchronize at different rates; the sleep-wake clock realigns within 2-3 days while the body temperature clock takes 5 or more days to realign.
- Not all rhythms resynchronize the same way. Rhythms can shift by either an advance or delay; so while some advance until they are resynchronized others will delay. This can prolong the feeling of jet-lag due to greater internal desynchronization.
Explain, to the extent we discussed in class, how the molecular circadian clock works. What molecules/proteins are involved? How do they interact with each other within the neural mechanisms of the cells in the SCN to measure time in 24 hour intervals.
Transcription factors (CLOCK, Bmal1/CYCLE) that transcribe DNA and RNA exist within the cells of the SCN. Glutamate binds to receptors that activate the binding protein that will bind to CLOCK and CYCLE together, when light is input via the SCN. CLOCK and CYCLE dimerize to transcribe the Per and Cry genes into mRNA.
RNAs are transported to the cytoplasm of the cell to be translated into proteins (Per and Cry). When the proteins accumulate, they dimerize and move back into the nucleus to inhibit the production of CLOCK and CYCLE, which shuts down their own production.
Over time, the dimerized Per and Cry proteins degrade in the cytoplasm and in the nucleus. Once they degrade in the nucleus CLOCK and CYCLE can begin transcribing the Per and Cry genes to start the cycle over.
The cycle takes ~24 hours and can be entrained . The peak of the dimerized Per and Cry proteins in the cytoplasm is midday while the trough is midnight. The cycle is turned on by light.
What is SAD? What are its symptoms? What are the circadian rhythm abnormalities that exist in SAD? What are the best interventions
Seasonal Affective Disorder: a type of depression related to changes in season. Beginning with and ending around the same time every year; usually symptoms begin in the fall through the winter and end in the spring.
Symptoms:
Depression symptoms occurring during the fall or winter months.
Full remission from depression in spring and summer months.
Symptoms occurred for past 2 years, with no non-SAD
Craving sugary/sweet foods
CR Abnormalities:
Phase delays in cortisol and melatonin
increases in minimum body temperature and phase delay of rhythm
Phase delay of sleep-wake cycle
Increased daytime levels of melatonin in winter
Best Interventions:
Light therapy–> works for most but not all
SSRIs phase advance activity of SCN neurons to increase expression of CLOCK and CYCLE.
Often SSRIs and light therapy are used in conjunction if light therapy isn’t enough
