Study your flashcards anywhere!

Download the official Cram app for free >

  • Shuffle
    Toggle On
    Toggle Off
  • Alphabetize
    Toggle On
    Toggle Off
  • Front First
    Toggle On
    Toggle Off
  • Both Sides
    Toggle On
    Toggle Off
  • Read
    Toggle On
    Toggle Off
Reading...
Front

How to study your flashcards.

Right/Left arrow keys: Navigate between flashcards.right arrow keyleft arrow key

Up/Down arrow keys: Flip the card between the front and back.down keyup key

H key: Show hint (3rd side).h key

A key: Read text to speech.a key

image

Play button

image

Play button

image

Progress

1/39

Click to flip

39 Cards in this Set

  • Front
  • Back
1. All of the following are involved with mammalian photoperiodism except the
a. Pineal gland
b. Suprachiasmatic nucleus (SCN)
c. GnRH neurons
d. Hippocampus
d. Hippocampus
2. The Aschoff Effect states that:
b. all circadian rhythms cycle at about 24 h
A phase response curve (PRC) best describes:
b. a rhythm's entrainment properties
4. Which of the following exhibits clock properties in birds?
a. Suprachiasmatic nucleus
b. Pineal gland
c. The retina of the eye
d. both a and b
e. a, b, and c
e. a, b, and c
5. In general, seasonal reproduction in various avian and mammalian species is usually regulated by one of the following factors, but not..
a)photoperiiod
b)food availability
c) a circanual rhythm
d) temp
d. temperature
6. The critical feature of pineal gland function that causes short-day-induced gonadal regression in rodents is:
a. the duration of the daily melatonin rhythm
7. What is photoperiodism?
b. the ability to use day length to time annual cycles
8. Biological clocks are involved in all of the following events, except
a. the sun-arc hypothesis
b. photoperiod time measurement
c. night orientation to star patterns
d. the hibernation cycle of the ground squirrel
e. the feeding cycles of voles
c) night orientation to star patterns
9. Infradian rhythms refer to those rhythms with a period
a. of 24 hours
b. that is less than 24 hours
c. that is more than 24 hours
d. of 1 year
c) that is more than 24 hrs.
10. What is the single-most defining characteristic of a true biological rhythm?
a. that it can be entrained by environmental cues
b. that it is self-sustaining
c. that it requires a zeitgeber
d. all true biological rhythms are circadian
b) self sustaining
What would be the effect of 30 minutes of light on a hamster's wheel running behavior if the hamster was kept in total darkness and the behavior was free-running?
wheel running marks onset of subjective night
so light preceeds onset of subj night = light has occured at the beginning of subjective night and this means phase delay.
Light exposure during photoinductive phase of circadian cycle evokes long day effects
If no light during photoinductive phase, then short day effects are obtained
Light exposure during photoinductive phase of circadian cycle evokes long day effects
If no light during photoinductive phase, then short day effects are obtained
What would one expect to happen if the zeitgeber was removed from a group of rats?
individual rats would be active consistently earlier or later every day
13. Which of the following statements is false?
a. melatonin at high doses (>100 mg) is toxic
b. the precursor for melatonin is serotonin
c. melatonin may inhibit aging
d. melatonin activates glutathione peroxidase
. melatonin at high doses (>100 mg) is toxic
14. If a male hamster is kept in short days (10 hrs light & 14 hrs dark) indefinitely, it will..
d. spontaneously exhibit testicular growth after several months?
15. Mammals, flies, fungi and cyanobacteria all have transcriptional clocks that work in a similar way, although has a different pair of genes. In mammals, the genes are
BMAL/Clock
Per and CRY
16 Photoperiodism in different organisms affects the timing of different physiology, but the one that is most universally affected is:
e. reproduction.
"Photo" of photoperiodism refers to :
c. light
18 IF you had a plant that was being consumed by a fast reproducing bug called bugerosus, and you found on the internet that the critical dark period for bugerosus' reproductive cycle is 5 hours, then you could conceivably control the bug by :
d. Leaving the lights on for 20 hours each day and off for 4 hours
19. The testes eventually develop in male hamsters even if they are not given the critical photoperiod. This observation demonstrates that testicular development is also controlled by:
d. a circannual rhythm.
Bright daylight can influence:
a. Amount of melatonin secreted in humans
b. Phase of onset of melatonin secreted in humans
c. Phase of onset of activity in hamsters
d. All of the above
all
. If free running hamsters in constant lighting conditions are given a light pulse during the middle of the subjective day, this will:
have little or no effect on the activity rhythm
22. Rodents are most likely to become arrhythmic (non-rhythmic) when exposed to:
continuous light
23 If you wanted to estimate the limits of entrainment to light/dark cycles for a particular species, which of the following would provide helpful information:
b. the phase response curve and tau
If free running hamsters in constant lighting conditions are given a light pulse during the middle of the subjective day, this will:
have little or no effect on the activity rhythm.
Briefly describe and evaluate the experimental evidence that the SCN is an important neural clock in mammals. In the second part of your answer propose what you think is the most important next step to understand SCN function as a neural pacemaker. Defend your choice and provide a brief experimental approach as to how you would address the problem.
Slices from the SCN maintain circadian rhythms of electrical activity
SCN transplants cause recipient's rhythm to match that of donor
Environmental light entrains oscillations of SCN

When you sever the SCN and activity changes, what is this called? splitting

SCN is master pacemaker, innervated by RHT

SCN receives input from RHT and IGL

Regulatory function - The SCN is able to regulate the secretion of melatonin

If you take the SCN out of its host, what will happen to the mechanism by which it fires? Nothing. If you take out the SCN it will still fire in a rhythmic manner.
2. Explain the essential elements of how the mammalian molecular clock works.
Given your general knowledge of clock properties, what do you see as the next important question to address regarding this molecular model? Defend your position. In general terms, how would you experimentally address the question?
in drosophillia, PER/TIM complexes enter the nucleus (in the middle fo the night)and some interact with CYC/CLOCK, resulting in the repression of transcription of the per and tim genes. sun will cause per molecules to degrade, releasing the inhibition. As PER protein is synthesized in the cytoplasm,
doubletime causes the degradation of PER proteins

Activated cryptochrome interacts with TIM, causing it to degrade

**
Conversely, in the mammalian clock, the process is such that PER/CRY complexes enter the nucleus to inhibit BMAL1/CLOCK.
**
Discuss the components of the oscillator that are associated with the mamalian clock. Negative Loop
Transcription of Period (mPer1-3) and Cryptochrome (mCry1-2) are regulated by the transcription factors BMAL1 and CLOCK
As mPER and mCRY are translated the reenter the nucleus and inhibit BMAL1/CLOCK

Positive Loop
mPER2 contributes to the transcription of Bmal1 180° out of phase with mPer/mCry
An increase in Bmal1 = more BMAL1/CLOCK, thereby resetting the cycle
Discuss the "negative loop" associated with the mamalian clock. Transcription of Period (mPer1-3) and Cryptochrome (mCry1-2) are regulated by the transcription factors BMAL1 and CLOCK
As mPER and mCRY are translated the reenter the nucleus and inhibit BMAL1/CLOCK
In the mamalian neg feedback loop, as mPER and mCRY are translated the reenter the nucleus and inhibit... BMAL1/CLOCK
In mammals, the transcription of period (per) and cytochrome (CRY) are regulated by what two transcription factors? Transcription of Period (mPer1-3) and Cryptochrome (mCry1-2) are regulated by the transcription factors BMAL1 and CLOCK
Discuss the positive loop in mamals. Positive Loop
mPER2 contributes to the transcription of Bmal1 180° out of phase with mPer/mCry
An increase in Bmal1 = more BMAL1/CLOCK, thereby resetting the cycle
3. Discuss the properties of a circannual rhythm. Provide examples of how circannual rhythms are important in biological systems. Evaluate our current understanding of these rhythms as well as what we do not know about them. Finally, suggest a future area of research and defend your answer.
Circannual Seasons of the year
365.25 days (300-400 days)

"An endogenous circannual rhythm drives the seasonal reproductive cycle of a broad spectrum of species. This rhythm is synchronized to the seasons (i.e., entrained) by photoperiod, which acts by regulating the circadian pattern of melatonin secretion from the pineal gland"

photoperiodism includes the ability to determine day length (usually by measuring night length) in both plants and animals.

Among vertebrate animals, photoperiodism is linked to a number of seasonal adaptations, including reproductive, metabolic, immunological, and morphological adaptations to cope with seasonal changes in ambient conditions.

photoperiodism = Thus, Rowan concluded that the number of hours of light per day, not ambient temperature or food availability, regulated the annual breeding cycle of juncos.
4. What is the experimental evidence that seasonal photoperiodism in mammals is circadian-based?
This info is in lectures 13 and 14
Tests for involvement of circadian system in photoperiodic time measurement (PTM)=
T-cycle experiments:
Use of 24 h vs non-24 h light:dark T-cycles
Photoperiodic induction (long day response) depends on circadian phase relationship between light and internal circadian rhythm (CT)
Determining the photoinducible phase

``
Circadian models---light inductive if present at certain times in circadian cycle
Note similarity to mechanism for phase shifting (entraining) actions of light

****Circadian involvement in photoperiodic time measurement (PTM)
Night-break experiments
Skeleton photoperiods
Resonance (Nanda-Hamner) paradigm
T-cycle experiments***

Resonance (Nanda-Hamner) paradigm:
Elliott exposed different groups of hamsters to 6L:18D, 6L:30D, 6L:42D, 6L:54D
Testis regression in 6L:18D and in 6L42D
Testis stimulation in 6L:30D and in 6L:54D
The results seem to rule out all of the hourglass models, but compatible with a circadian model
Note that one long day/week was sufficient to stimulate reproduction in hamsters

Determining the photoinducible phase
Bunning’s hypothesis: An entrainable circadian cycle with two 12-hour components that vary in their responsiveness to light exists
Photo-noninducible and photoinducible phases
When animals first encounter light, the 12 h photo-noninducible phase is set.
Light exposure during the next 12 h will not affect long-day, photoperiodic responses
Only when light is coincident with the following 12 h photoINDUCIBLE phase will a long-day photoperiodic response occur.

External coincidence
Light exposure during photoinductive phase of circadian cycle evokes long day effects
If no light during photoinductive phase, then short day effects are obtained
Internal coincidence
Phase relationships between two circadian oscillators (dusk and dawn oscillators?) determine photoperiodic time measurement (PTM)
5. Define and give the physiological significance (how or why it is important) for 3 of the following 4 terms:
a. Non-photic entrainment:
an example of a nonphotic zeitgeber is motor activity

types of non-photic cues:
Circadian Control of Feeding
Food Entrainment
Environmental change
Locomotor activity
Social synchronization

"It is concluded that non-photic zeitgebers can entrain the rest-activity cycle in humans, which is independent of the circadian pacemaker."

"The effect of appropriately timed exercise or exogenous melatonin represents the
best proof to date of an effect of nonphotic stimuli on human circadian timing."
-not sure if this is all I need or not.
mammals is circadian-based?
5. Define and give the physiological significance (how or why it is important) for 3 of the following 4 terms:

b. Neuropeptide Y:
Neuropeptide Y is the neurotransmitter associated with the IGL.
(The IGL is important for entrainment, synchronization, nonphotic cues (like motor activity)).

associated with regulating energy balance and feeding
Define and give the physiological significance of RHT.
Light activates subset of retinal ganglia cells
Photic info reaches SCN via the monosynaptic RHT pathway.

Release of Glutamate from RHT terminals may activate different signaling pathways that are associated with the oscillator
Describe and give the physiological significance of NAT(how or why important):
Deguchi (1978): Asked whether clock that controls pineal NAT rhythm is set independently of environmental light (no clock) or only set after newborn is exposed to LD cycle (presence of light, so clock required). What did he find? 1. Established regulation by internal biological clock
Showed that NAT rhythm of population phase delayed by about 3h/week when animals are in DD (so tau must be close to 24.5h)
2. Deguchi considered possibility that pups perceived LD cycle before birth (by light penetrating abdominal wall of mother)---to test this:
He put adult pair of rats in DD 10 days before mating and keep mother in DD during pregnancy and after birth of pups
Measured pups' NAT at 23 days of age
Phase of rhythm delayed several hours as compared to previous study---could be because mother was being delayed from time she went into DD and she entrains pups
3. He also used mothers from original LD cycles that were 180 degrees out-of-phase with each other
If pups were switched between the two types of mothers on day of birth, their pineal NAT rhythms were intermediate to the phases of unswitched pups---This an important observation in that it indicates both prenatal and postnatal influence of mother rats on circadian phase of pups' rhythms
4.By using blinded mothers, he showed that pups could be synchronized to LD cycles by 10 days after birth
6. Describe the two ways that biological clocks allow animals to adapt to temporal fluctuations.
Discuss the temporal organization of bio clocks. They control an organisms’ behavior and activities so that they occur at the "right time".
For example, clocks coordinate when males and females of the same species become fertile so that the period of maximum fertility coincides, thus establishing a breeding season.
In cyanobacteria (blue-green algae), there is both photosynthesis and nitrogen fixation but the latter process cannot occur in the presence of oxygen.
These processes therefore need to be separated.
Under the control of a biological clock these 2 processes are temporally segregated: photosynthesis occurs during the day, fixation during the night

Temporal Organization between Species.
Biological clocks function such that certain species are active, for example, during the day, while others are active during the night.
If a prey species is active during the night, then the clock of its predator will ensure it “wakes up" so it does not miss out on a potential meal.
In the same way, prey species may become active at times when the predators are usually not active (to avoid becoming a meal!)

note that A zeitgeber is any environmental factor that provides a temporal cue.




Evolution of Biological Clocks


Anticipation of an Organisms Environment.
By registering local time and events (such as high and low tide), biological clocks allow organisms to prepare for and anticipate their environment.
Predictive Homeostasis is a good example of this –
an organism can activate certain systems preempting the changes that will occur in the environment e.g. in humans cortisol levels are raised before we wake up, increasing the metabolic rate so we have the energy necessary for the day ahead
8. EXPLAIN an example of how PREDICTION is an important factor for an organism having photoperiodic capabilities.
photoperiodism includes the ability to determine day length (usually by measuring night length) in both plants and animals.
The biological ability to measure day length permits organisms to ascertain the time of year and engage in seasonally-appropriate adaptations (see seasonal reproduction).

individuals that respond to day length can precisely, and reliably, ascertain the time of year with just two bits of data:
(1) the length of the daily photoperiod
(2) whether day lengths are increasing or decreasing.

Thus, Rowan concluded that the number of hours of light per day, not ambient temperature or food availability, regulated the annual breeding cycle of juncos.
photorefractory
photorefractory =
during the recrudescent phase; i.e., gonadal condition becomes unlinked from photoperiodic inhibition.

Photorefractoriness permits attainment of fully functional gonads in the spring before environmental photoperiods attain 12.5 h, the day length necessary for gonadal maintenance in the autumn.
Seasonality via photoperiodism
Example of Type I annual rhythm: hamster annual cycles
Photosensitive phase
(Photoresponsive)
Photorefractory phase---
(Photorefractory)

photorefractory during the recrudescent phase; i.e., gonadal condition becomes unlinked from photoperiodic inhibition.
Photorefractoriness permits attainment of fully functional gonads in the spring before environmental photoperiods attain 12.5 h, the day length necessary for gonadal maintenance in the autumn.
hourglass model of photoperiodism
According to the first model, animals monitor the accumulation (or depletion) of some physiological agent during one part of the light-dark cycle
This process is reversed during another portion of the cycle.
Discuss how the resonance experiments ruled out the hourglass model
Resonance (Nanda-Hamner) paradigm:
Elliott exposed different groups of hamsters to 6L:18D, 6L:30D, 6L:42D, 6L:54D
Testis regression in 6L:18D and in 6L42D
Testis stimulation in 6L:30D and in 6L:54D
The results seem to rule out all of the hourglass models, but compatible with a circadian model
Note that one long day/week was sufficient to stimulate reproduction in hamsters