Final Exam

Question 1

What is the temporal relationship between per gene expression and PER protein levels in fruit flies? In mammals?

Answer 1

in both fruit flies and mammals, there’s a cyclic relationship between PER gene expression (making mRNA) and the levels of PER proteins. The gene produces mRNA, which leads to the creation of proteins. These proteins accumulate, inhibit their own gene’s activity, and then break down, allowing the cycle to start again.

Question 2

In fruit flies, on what clock gene or protein does light act to cause phase shifts, and how does light affect that gene or protein?

Answer 2

In fruit flies, light acts on a clock gene called “period” (per) to cause phase shifts. Light affects this gene by regulating the production of the PER protein. When flies are exposed to light, it can either speed up or slow down the production of the PER protein, causing changes in their internal biological clock.

Question 3

In mice, on what clock gene or protein does light act to cause phase shifts, and how does light affect that gene or protein?

Answer 3

In mice, light acts on a clock gene called “Clock Protrein” to cause phase shifts. Light exposure impacts the activity of these proteins, which in turn affects the mouse’s internal clock.

Question 4

Can circadian clocks operate without gene transcription, and if so, what is the evidence?

Answer 4

Yes, circadian clocks can operate without gene transcription. Some evidence comes from experiments using cyanobacteria. These organisms have a clock-like system that functions without gene transcription. Researchers found that even when they halted gene expression, the circadian rhythm continued, indicating that the clock can work independently of gene transcription. This suggests the presence of post-translational processes, such as protein modifications, that sustain the circadian rhythm without new gene activity.

Question 5

The circadian clock is said to be ‘cell autonomous’ – what does that mean, and what is the evidence?

Answer 5

“Cell autonomous” means that each cell possesses its own independent circadian clock. This clock allows the cell to regulate its functions, like metabolism, independent of signals from other cells or the body. Evidence for this comes from experiments where cells kept in isolation maintain their circadian rhythm, showing that they continue to follow their internal clock without external cues from the body or other cells.

Question 6

Is there a circadian clock in the olfactory bulb? If so, does it cycle ‘in phase’ with the SCN pacemaker (i.e., showing peaks and troughs at the same time as the SCN). Does it require the SCN circadian pacemaker to cycle?

Answer 6

Yes, the olfactory bulb has its own circadian clock. It does cycle in phase with the master clock in the brain called the suprachiasmatic nucleus (SCN). However, the olfactory bulb’s clock can operate independently, but it can also be influenced by signals from the SCN, suggesting a connection between the two clocks.

Question 7

Knockout of the gene Bmal1 has what effect on circadian rhythms in mice?

Answer 7

Knocking out the gene Bmal1 leads to having no circadian limits to entrainment of food. These mice don’t rely on the typical daily patterns to know when to eat. They’re not restricted by the usual time cues; they can adapt to eating at any time, without following the usual 24-hour cycle like normal mice do.

Question 8

Are there circadian clocks in peripheral organs and tissues (e.g., liver, pancreas, etc) and if so, what stimuli are they entrained by, and what role does the SCN pacemaker play?

Answer 8

Yes, there are circadian clocks in peripheral organs like the liver, pancreas, and others. They can be entrained by cues like meal timing, temperature changes, and hormone levels. The SCN pacemaker in the brain acts as the master regulator, coordinating these peripheral clocks to keep them synchronized with the overall day-night cycle and ensuring harmony among different organ rhythms.

Question 9

Why do circadian activity rhythms damp out in nocturnal rodents maintained in constant light for many weeks? What effect does constant light have on individual circadian clock cells in the SCN?

Answer 9

Constant exposure to light can cause dampening of circadian activity rhythms in nocturnal rodents over time because their internal biological clocks lose their regularity and synchronization. In the SCN, individual circadian clock cells start to desynchronize, affecting their coordination and leading to disrupted rhythms seen in behavior and activity patterns.

Question 10

In mice, what effect does Per protein have on Bmal1? Does it affect Bmal1 gene expression, or does it affect how Bmal1 protein activates the per and cry genes?

Answer 10

The Per protein in mice affects Bmal1 by inhibiting its activity. Per doesn’t directly affect Bmal1 gene expression but instead interferes with how Bmal1 protein activates the per and cry genes, creating a feedback loop that regulates the circadian clock.

Question 11

If the SCN pacemaker is made up of several thousand individual circadian clock cells, what happens to circadian activity rhythms if those cells become desynchronized from each other?

Answer 11

This desynchronization can lead to irregular and fragmented activity patterns rather than the usual organized daily rhythms.

Question 12

Following a shift of the LD cycle, do circadian clocks in different brain and body parts re-entrain at the same rate or at different rates?

Answer 12

The master clock in the brain, the (SCN) plays a crucial role in coordinating these rhythms throughout the body. When there’s a shift in the light-dark cycle, the SCN adjusts to the new timing and helps to re-establish the rhythms in other organs and tissues.

Heart, liver, and other tissues may take a bit longer to fully re-entrain

Question 13

What role do rods and cones play in entrainment of the circadian clock by light in mammals? Are they necessary (no entrainment without rods and cones)? Are they sufficient (entrainment is possible with only rods and cones)?

Answer 13

Rods and cones in the eyes play a crucial role in entraining the circadian clock by detecting light. They are necessary for entrainment, meaning without rods and cones, you’d lose the ability to see objects or movement. They need ganglion cells to be sufficient

Question 14

What role does the photopigment melanopsin play in entrainment of the circadian clock by light in mammals? Is it necessary? Is it sufficient? What cells in the retina contain melanopsin?

Answer 14

Melanopsin is crucial for entrainment of the circadian clock in mammals. It’s necessary because it helps transmit light information to the brain’s circadian system, particularly in low-light conditions. While melanopsin is essential, it’s not sufficient on its own for entrainment. It’s primarily found in a specific type of retinal cells These cells contribute significantly to signaling light information to the brain for regulating the circadian rhythm.

Question 15

What are ‘intrinsically photoreceptive retinal ganglion cells’ and what is their relationship with rods and cones?

Answer 15

Intrinsically photosensitive retinal ganglion cells (ipRGCs) are a unique type of cells in the retina that can directly sense light, unlike rods and cones. While rods and cones are the main visual cells, ipRGCs have their own light-sensitive pigment called melanopsin, allowing them to detect light levels and play a specific role in regulating the body’s internal clock, the circadian rhythm. They work alongside rods and cones but have a distinct function in signaling light information for non-visual processes like regulating sleep-wake cycles.

Question 16

Intrinsically photoreceptive retinal ganglion cells have many dendrites that form a wide net-like pattern. Form determines function, and sometimes we can infer what a neuron does based on what it looks like. What does the broad, net-like dendritic tree of these neurons imply about what these ganglion cells can communicate about light. Would they be useful for counting photons (signalling daytime) or would they have any use for object recognition?

Answer 16

The broad, net-like dendritic tree of intrinsically photoreceptive retinal ganglion cells suggests they’re specialized for capturing overall ambient light levels rather than details or shapes. This structure implies they’re more suited for signaling changes in overall brightness, like distinguishing between day and night (counting photons), rather than recognizing specific objects or details in the visual environment.

Question 17

Which wavelength (and associated colour) of light is most effective for inducing phase shifts?

Answer 17

Short-wavelength blue light is the most effective for inducing phase shifts in the circadian rhythm

Question 18

The direct projection from the retina to the suprachiasmatic nucleus is called the____________

Answer 18

The direct projection from the retina to the suprachiasmatic nucleus is called the “retinohypothalamic tract.”

Question 19

In the mouse circadian clock, activation of retinal photoreceptors by light causes release of which neurotransmitter in the suprachiasmatic nucleus?

Answer 19

neurotransmitter

Question 20

The neurotransmitter (answer to previous question) that is released in the SCN in response to light has what effect on SCN neurons?

Answer 20

The neurotransmitter glutamate, released in response to light in the SCN, excites and activates SCN neurons, playing a key role in transmitting light signals to regulate the circadian clock.

Question 21

Lesions to which of the following structures consistently block phase shifts induced by exercise in Syrian hamsters?

Answer 21

Lesions to the intergeniculate leaflet (IGL) consistently block phase shifts induced by exercise in Syrian hamsters.

Question 22

A neurotoxin that kills 5HT (serotonin) neurons in the mouse brain has what effect on circadian rhythms

Answer 22

Mice with these lesions failed to entrain to a daily exercise schedule.

Question 23

Neurons in the intergeniculate leaflet are activated by what type of stimulus, and are important for entrainment to what kind of time cues?

Answer 23

Neurons in the intergeniculate leaflet (IGL) are activated by changes in ambient light levels and are crucial for entrainment to non-image-forming time cues, especially those related to the timing of dawn and dusk.

Question 24

In hamsters, the phase shifting effect of exercise in the usual sleep period can be mimicked by injection of which neurochemical into the SCN?

Answer 24

Injecting glutamate into the suprachiasmatic nucleus (SCN) of hamsters mimics the phase-shifting effect of exercise during the usual sleep period.

Question 25

Do neurons in the dorsal and median raphe project directly or indirectly to the SCN pacemaker?

Answer 25

Neurons in the dorsal and median raphe project indirectly to the SCN pacemaker, often connecting through other brain regions before reaching the suprachiasmatic nucleus (SCN).

Question 26

Does melatonin induce phase shifts in mammals, and if so, is the phase response curve similar to the PRC for light, for exercise, or for neither?

Answer 26

Melatonin can induce phase shifts in mammals, but its phase response curve is different from both light and exercise. It follows its own distinct pattern in influencing the circadian rhythm.

Question 27

Which of the following is a possible mechanism for ‘radio broadcasting’ of circadian signals from an SCN graft?

Answer 27

One possible mechanism for the 'radio broadcasting' of circadian signals from an SCN graft is through its ability to synchronize and communicate with the recipient brain tissue by sending out rhythmic signals that influence the recipient's circadian rhythms. This synchronization happens via neural connections and chemical signaling between the grafted SCN and the host brain.

Question 28

Tetrodotoxin blocks sodium channels in neurons. What effect does this have on activity of those neurons? What effect does it have on circadian activity rhythms if infused into the SCN?

Answer 28

Tetrodotoxin stops neurons from firing by blocking their sodium channels. When infused into the SCN, it disrupts the normal functioning of SCN neurons, causing disturbances in circadian activity rhythms.

Question 29

Cutting SCN axonal outputs by circular knife cuts has what effect on circadian rest-activity rhythms? Are there species differences in the effect?

Answer 29

Cutting SCN axonal outputs through circular knife cuts disrupts circadian rest-activity rhythms. The impact can differ among species, but generally, it causes significant disturbances in the normal sleep-wake cycles.

Question 30

Can SCN transplants restore circadian rhythms in arrhythmic animals that lack studies tell us that direct axonal projections from the SCN to one or more other hypothalamic areas are necessary for some but not all circadian rhythms.

Answer 30

SCN transplants can restore circadian rhythms in animals that lack their own rhythms. Studies suggest that direct axonal projections from the SCN to specific hypothalamic areas are necessary for certain circadian rhythms, but not all rhythms rely solely on these connections

Question 31

Do animals with an SCN lesion sleep more, less or the same amount as intact animals? Does it depend on the species? Do lesions affect how much animals sleep after they have been sleep deprived for 24h?

Answer 31

Animals with an SCN lesion can sleep more, less, or the same amount compared to intact animals, depending on the species. Lesions can affect how much sleep animals get after being sleep-deprived for 24 hours, altering their recovery sleep patterns.

Question 32

After 24h sleep deprivation does the amount of recovery sleep depend on the time of day that the deprivation ends, or is this ‘homeostatic’ response completely independent of time of day (circadian phase)?

Answer 32

Animals with an SCN lesion can sleep more, less, or the same amount compared to intact animals, depending on the species. Lesions can affect how much sleep animals get after being sleep-deprived for 24 hours, altering their recovery sleep patterns.

Question 33

* What is a ‘tau mutant’ hamster?

Answer 33

A tau mutant hamster is a special type of hamster with a mutation that causes its circadian rhythm to have a different natural cycle length (tau) compared to normal hamsters. This mutation affects the duration of its daily rhythms, altering the timing of its sleep-wake cycle.

Question 34

If a wildtype Syrian hamster receives a partial SCN lesion and then receives an SCN transplant from a tau mutant hamster, what does its circadian activity rhythm look like? Does it look like a wildtype, a tau mutant, or both? If both, is one phase of the circadian rest-activity cycle dominant, or are they equivalent in strength (which begs the question, is it even possible for both phases of the rest-activity cycle to be equivalent in strength)?

Answer 34

When a wildtype Syrian hamster with a partial SCN lesion receives an SCN transplant from a tau mutant hamster, its circadian activity rhythm can exhibit characteristics of both wildtype and tau mutant rhythms. Sometimes, one phase might dominate, while in rare cases, both phases might appear equally strong, but it's uncommon for both phases to be entirely equivalent in strength.

Question 35

According to the Opponent Process model of sleep regulation, SCN output has what effect on sleep and wake states?

Answer 35

In the Opponent Process model, SCN output promotes wakefulness and inhibits sleep, contributing to the regulation of the sleep-wake cycle by favoring alertness during the day and initiating sleep at night.

Question 36

How might a genetically fast or slow running circadian clock be a cause of sleep onset or sleep maintenance insomnia?

Answer 36

A genetically fast-running circadian clock might cause sleep onset insomnia by making it challenging to fall asleep at the desired bedtime. Conversely, a slow-running clock could lead to sleep maintenance insomnia by causing difficulties in staying asleep throughout the night. These variations can disrupt the alignment between the body's internal clock and the external day-night cycle, affecting sleep patterns.

Question 37

Is the duration of individual REM sleep episodes constant throughout the night, or does it depend on circadian phase?

Answer 37

The duration of individual REM sleep episodes can vary throughout the night and might depend on the circadian phase. Typically, REM episodes become longer as the night progresses, especially during later sleep cycles.

Question 38

At what circadian phase (or time of day) is sleep ‘propensity’ (the likelihood of falling asleep) highest and lowest, or does the circadian clock not regulate sleep propensity?

Answer 38

Our bodies have a natural rhythm called the circadian clock that helps regulate sleep. Generally, the highest likelihood of falling asleep, or sleep propensity, happens during the late evening and early night when our body's internal clock tells us it's time to rest. This is when we feel most sleepy. The lowest sleep propensity occurs during the morning when our bodies are set to be awake and alert. So, yes, the circadian clock does influence our likelihood of falling asleep!

Question 39

Under normal conditions, when is the homeostatic drive for sleep highest and lowest?

Answer 39

The homeostatic drive for sleep is like a built-up need for rest that increases the longer we're awake. So, the highest homeostatic drive for sleep usually happens the longer you've been awake, making you feel more and more tired. After a good night's sleep, this drive is at its lowest because you've had the rest your body needed.

Question 40

Intuitively, it would seem that the longer we have been awake, the longer we would need to sleep to recover. Is this true, or does the circadian clock determine how longer humans sleep, or do both factors contribute to sleep duration? How has this been tested, and what are the findings (discussed in the module on circadian regulaton of sleep in humans).

Answer 40

Both the time we've been awake (homeostatic drive) and our internal body clock (circadian rhythm) influence how long we sleep. Studies show that after being awake longer, we tend to feel a stronger need for sleep and might sleep longer to recover. However, our internal clock also plays a role in determining when we naturally feel sleepy and how long we sleep, even if we've been awake for different lengths of time. Researchers use various tests, like monitoring sleep patterns during different schedules, to understand how both factors affect sleep duration. They found that both the time awake and the body clock contribute to how long we sleep, and they work together to regulate our sleep patterns.

Question 41

In temporal isolation sleep onset in humans is most likely to occur near what circadian phase of the body temperature cycle?

Answer 41

In temporal isolation (when someone doesn't have cues from the outside world), sleep onset in humans is most likely to occur around the downward shift of the body temperature cycle, which happens in the evening and early night. This drop in body temperature helps signal the body that it's time to wind down and get ready for sleep

Question 42

In temporal isolation sleep duration in humans is longest when sleep begins at what circadian phase of the temperature cycle?

Answer 42

In temporal isolation, when sleep begins around the time of the body temperature's natural downward shift (usually in the evening/early night), humans tend to have their longest sleep duration. This aligns with our body's internal rhythms, allowing for a more extended and restful sleep.

Question 43

In humans, after a full day of sleep deprivation, which sleep stage shows the largest increase?

Answer 43

After a full day of sleep deprivation, the sleep stage that typically shows the largest increase when a person finally gets to sleep is the deep sleep stage, also known as slow-wave sleep. This stage tends to become more prominent and extended as the body tries to compensate for the lack of rest

Question 44

In humans, which if any sleep stage is most strongly controlled by the circadian clock?

Answer 44

Among the different sleep stages in humans, REM (rapid eye movement) sleep is most strongly influenced by the circadian clock. This stage tends to follow the body's internal clock rhythm more closely compared to other sleep stages.

Question 45

Sleep duration in temporal isolation, in humans showing spontaneous internal desynchrony, can be accounted for by these two factors:

Answer 45

In temporal isolation when people experience internal desynchrony, meaning their body clocks are out of sync, sleep duration can be influenced by two main factors: the body's internal clock (circadian rhythm) and the accumulated need for sleep (homeostatic drive). These factors together affect how long someone sleeps in such conditions.

Question 46

* At what time of day would the ‘wake maintenance zone’ normally occur?

Answer 46

The "wake maintenance zone" typically happens during the daytime, particularly in the late morning and early afternoon. This is when our bodies naturally feel more awake and alert, making it easier to stay awake and focused.

Question 47

* Is homeostasis of sleep duration critical to maintain a stable circadian sleep-wake rhythm?

Answer 47

Yes, maintaining a stable sleep duration through homeostasis is important to keep a consistent circadian sleep-wake rhythm. The body's need for sleep (homeostasis) helps balance and support the natural sleep-wake cycle regulated by the internal body clock (circadian rhythm).

Question 48

* Describe the Forced Desynchrony Protocol for studying human circadian rhythms. What is the purpose of using this protocol?

Answer 48

The Forced Desynchrony Protocol is a method used to study human circadian rhythms by disconnecting the body's internal clock from external time cues. People follow a schedule where their sleep-wake cycle doesn't match the 24-hour day. This helps researchers understand how our internal body clock affects things like sleep, alertness, and performance when it's not aligned with the natural day-night cycle. The purpose is to see how our internal clock influences different body functions when it's out of sync with the outside world.

Question 49

* The forced desynchrony protocol yielded a revised estimate of the free-running period of human circadian rhythms. Why was the original estimate, from humans free-running in temporal isolation, incorrect, and in what direction (longer or shorter)?

Answer 49

The original estimate of the free-running period of human circadian rhythms, found in temporal isolation, was incorrect because it was influenced by external factors accidentally affecting the body's internal clock. This led to an incorrect estimate that was shorter than the actual free-running period. The forced desynchrony protocol helped correct this by eliminating external cues, revealing a longer and more accurate estimate of the body's natural rhythm.

Question 50

* What did Peretz Lavie discover about sleep regulation from studies using an ultra-short sleep-wake cycle

Answer 50

Peretz Lavie discovered that even in ultra-short sleep-wake cycles (20-30 minutes awake followed by a short nap), the body can adjust and adapt to this pattern, entering deep sleep faster during the short naps. This finding showed that the body can efficiently regulate and access restorative sleep even within brief sleep intervals, challenging traditional ideas about sleep duration requirements.

Question 51

* Is there a plausible explanation for the difference in the free-running period (tau) between sighted people and circadian blind people? Tip: remember the lecture on entrainment by light, and the phenomenon of ‘aftereffects’ of entrainment, discovered in rodents.

Answer 51

The difference in the free-running period (tau) between sighted people and circadian blind individuals could be due to the way light entrains, or syncs, our internal body clocks. Sighted individuals' body clocks can be adjusted or entrained by exposure to light, which affects their free-running period. However, circadian blind individuals lack this entrainment due to their inability to perceive light, leading to a longer or different free-running period compared to sighted individuals. This difference is linked to how our body clocks respond to light cues for regulation.

Question 52

* In humans, reaction time on tests of vigilant attention is fastest at what circadian phase?

Answer 52

Reaction time on tests of vigilant attention is typically fastest during the late morning to early afternoon, around the peak of the wakefulness phase in the circadian cycle.

Question 53

* Does chronotype (evening vs morningness) have any influence on academic performance, in studies of large numbers of high school and/or college students?

Answer 53

Yes, studies with large groups of high school and college students suggest that chronotype, whether someone is more of a morning or evening person, does indeed influence academic performance. Morning-oriented individuals tend to perform better academically compared to their evening-oriented counterparts. This difference is often attributed to the alignment between their natural body clocks and the typical schedules of school or college, which can affect attention, alertness, and overall performance.

Question 54

* Why are later school start times recommended for high school students?

Answer 54

Later school start times are recommended for high school students because their natural body clocks tend to favor later waking and sleeping schedules. By aligning school schedules more closely with their biological rhythms, students can get more sleep, which improves their attention, alertness, and overall academic performance. This adjustment also helps reduce issues related to sleep deprivation and allows students to be more productive during school hours.

Question 55

* What is social jetlag? Does it tend to differ in morning and evening types?

Answer 55

Social jetlag refers to the mismatch between our body's internal clock (circadian rhythm) and our social schedules, like work or school timings. It happens when we follow different sleep schedules on weekdays versus weekends, causing a "jetlag-like" feeling. Morning types often experience social jetlag if they stay up late on weekends, while evening types might experience it if they have to wake up early during the week, disrupting their natural sleep patterns.

Question 56

* To maximize sleep duration between night shifts, a shiftworker returning home from the night shift should go to sleep at what time (immediately, later, or does it matter)?

Answer 56

To maximize sleep duration between night shifts, a shift worker returning home from the night shift should aim to go to sleep as soon as possible after finishing work. This allows for more uninterrupted sleep and better alignment with their body's natural sleep patterns.

Question 57

* Differences in accident rates between day and night work are primarily due to what factors?

Answer 57

Differences in accident rates between day and night work primarily occur due to factors like fatigue, reduced alertness, and the body's natural inclination for sleep during the night. Night workers often experience sleep disruptions, leading to decreased attention and reaction times, which can contribute to higher accident rates compared to day work.

Question 58

* The most common complaint of shiftworkers is_______________________

Answer 58

The most common complaint of shift workers is usually related to sleep problems, like insomnia or feeling tired despite sleeping

Question 59

* Health problems associated with shiftwork are thought to be caused by what factor(s)?

Answer 59

Health problems associated with shift work are believed to be caused by disruptions to the body's natural sleep-wake cycle. Factors like irregular sleep patterns, circadian rhythm disturbances, and the mismatch between biological clocks and work schedules contribute to various health issues among shift workers.

Question 60

* Do health problems associated with shiftwork get worse over time, or does this vary in different people?

Answer 60

Health problems related to shift work can vary among individuals. For some, these issues may worsen over time due to ongoing disruptions to sleep and the body clock. However, the extent to which problems worsen can differ based on factors like individual resilience, coping strategies, and the specific nature of the shift work schedule.

Question 61

* In sporting events, if one team has to travel east by 3 time zones to play an evening game, is that team at a disadvantage or an advantage from a circadian rhythm perspective, and does this advantage or disadvantage get better or worse the later the game goes?

Answer 61

When a team travels east by three time zones for an evening game, they are at a disadvantage from a circadian rhythm perspective. Their body clocks are still aligned with the time at their home location, making it harder for them to perform optimally. This disadvantage tends to worsen as the game gets later because their body clocks signal sleepiness, affecting performance more as the night progresses

Question 62

* What kind of sleep problems are we most likely to have immediately after flying 3 times zone east?

Answer 62

After flying three time zones east, the most common sleep problem people experience is difficulty falling asleep at the new local bedtime. This occurs because your body's internal clock is still synced with your home time zone, making it harder to fall asleep at the earlier local time.

Question 63

* Is napping in the middle of a night shift a good strategy to minimize errors and accidents? Are there potential adverse effects?

Answer 63

Napping during a night shift can help reduce errors and accidents by providing a short burst of rest. However, it might affect the quality of nighttime sleep after the shift and could potentially disrupt the body's natural sleep pattern, causing confusion in the body clock. So, while it can offer a quick energy boost, it might affect overall sleep quality and rhythm.

Question 64

* The World Health Organization has classified shiftwork as a ‘probable carcinogen’. What is the main evidence?

Answer 64

The classification by the World Health Organization (WHO) is based on evidence suggesting that prolonged exposure to night shift work disrupts the body's natural sleep patterns and circadian rhythms. This disruption has been linked to potential health risks, including an increased likelihood of developing certain types of cancer, particularly breast cancer in women, due to the disturbance in hormonal cycles and light exposure during the night.

Question 65

* Light at night is hypothesized to be a possible cause of cancer in shiftworkers. Are there specific hypotheses concerning the mechanism by which nocturnal light exposure could do this?

Answer 65

Exposure to light at night, especially artificial light, might disrupt the body's production of melatonin. Melatonin is a hormone that helps regulate our sleep-wake cycle and has protective effects against cancer. Reduced melatonin due to nighttime light exposure could interfere with the body's ability to fight off cancerous cell growth, potentially raising the risk of developing certain cancers in shift workers.

Question 66

* Is there a single best shift schedule rotation? Is there a worst rotation?

Answer 66

There isn't a single best shift schedule for everyone, as different schedules suit different people based on their sleep patterns and preferences. However, rotating shifts in a clockwise direction (morning, afternoon, night) tends to be easier for most people to adapt to compared to frequent changes or abrupt shifts in schedules, which can be more challenging and disruptive to sleep and health.

Question 67

* Does the ability to tolerate or adapt better to night work depend on chronotype?

Answer 67

Yes, the ability to tolerate or adapt to night work can depend on an individual's chronotype, whether they are naturally inclined towards being a morning person or an evening person. People with a chronotype that aligns closer to night hours might find it easier to tolerate or adapt to night shifts compared to those who are naturally more inclined towards mornings.

Question 68

* The circadian clock typically does not shift very much during night work. Why not?

Answer 68

During night work, the circadian clock doesn't shift much because it's primarily influenced by light cues. At night, when the body expects darkness, exposure to artificial light can confuse the clock, but it doesn't cause a significant shift because the body's internal clock responds less to light during the night compared to the daytime. As a result, the clock doesn't adjust as much during night work, maintaining a more stable rhythm.

Question 69

* Is there a drug or nonphotic stimulus that has been shown to help circadian adjustment to night work?

Answer 69

Yes, there are some drugs, like melatonin supplements, and non-photic stimuli such as appropriately timed exposure to bright light or darkness, that have been studied for their potential to help adjust the body's circadian rhythm to night work. These can assist in facilitating adaptation to new schedules or aiding in shifting the body clock to align better with night shifts.

Question 70

* One strategy to adapt (shift the circadian clock) to permanent night work, is to control light exposure. When should the shiftworker seek light, and when should they avoid light, if they want to delay their circadian cycle by say 9-10 hours?

Answer 70

To delay their circadian cycle by 9-10 hours for permanent night work, shift workers should seek bright light exposure in the evening and early night when they want to stay awake and alert. They should avoid bright light exposure in the morning and during the day when they want their body to signal sleepiness and help shift their internal clock to a later time.

Question 71

* Performance on tests of attention is worst at what phase of the circadian cycle?

Answer 71

Performance on tests of attention tends to be worst during the early morning hours, typically around the hours just before and after natural wake-up time when our body's internal clock signals sleepiness.

Question 72

* Bipolar disorder has been linked to what type of rhythm, regulated by which neurotransmitter?

Answer 72

Bipolar disorder has been linked to disruptions in the circadian rhythm, which is regulated in part by the neurotransmitter serotonin. Changes in serotonin levels can affect the body's internal clock and contribute to the mood fluctuations seen in bipolar disorder.

Question 73

* Ultradian activity rhythms in common voles are adaptive in what way?

Answer 73

Ultradian activity rhythms in common voles are adaptive because they help these animals efficiently manage their energy and activities throughout the day. These shorter, repeated cycles allow them to balance periods of intense activity with rest, optimizing their survival strategies.

Question 74

* Are nocturnal animals with free access to food always nocturnally active?

Answer 74

No, nocturnal animals with free access to food aren't always active during the night. They might adjust their activity based on other factors like safety, social interactions, or environmental changes, even if they have food available.

Question 75

* Drinking ‘heavy’ water (D2O) slows (lengthens) what type of rhythms?

Answer 75

Drinking heavy water (D2O) tends to slow down or lengthen the circadian rhythms in biological systems

Question 76

* Syrian hamster gonads shrink in the fall because of changes in what environmental factor, which affects the level of what hormone?

Answer 76

Syrian hamster gonads shrink in the fall due to changes in the amount of daylight, which affects the level of melatonin hormone secreted by the brain's pineal gland.

Question 77

* What is it that causes Syrian hamster gonads to ‘spontaneously recrudesce’ (regrow) in the spring?

Answer 77

The longer days of spring cause the recrudescence, or regrowth, of Syrian hamster gonads. Increased daylight triggers a decrease in melatonin production, which stimulates the regrowth of their reproductive organs.

Question 78

* What do we mean by ‘Photorefractory’?

Answer 78

"Photorefractory" refers to a state where an organism becomes less responsive or resistant to changes in daylight or photoperiod, typically after being exposed to specific light conditions for a certain duration. It's a point where further changes in daylight don't have the same effect as before.

Question 79

* Annual rhythms are controlled by ‘photoperiodism’ or by ‘circannual’ clocks. What is the difference between these mechanisms?

Answer 79

Photoperiodism refers to the way organisms respond to changes in day length, influencing seasonal behaviors. Circannual clocks, on the other hand, are internal biological rhythms that naturally track yearly cycles, guiding seasonal changes even without external light cues. Photoperiodism relies on external light changes, while circannual clocks are internal rhythms that work independently to regulate annual patterns.

Question 80

* Lesions of which structure(s) eliminate(s) photoperiodism in rodents?

Answer 80

Lesions in the suprachiasmatic nuclei (SCN) can eliminate photoperiodism in rodents. These structures are crucial in processing light information and regulating the body's response to changes in day length. Damage to the SCN disrupts the ability to recognize changes in daylight, affecting the seasonal behaviors linked to photoperiodism.

Question 81

* Annual rhythms that are partly based on an hourglass type clock are called: ________________.

Answer 81

Annual rhythms that are partly based on an hourglass-type clock are called "circannual rhythms." These are biological patterns that follow an approximate yearly cycle, similar to an hourglass running through its course over a set period

Question 82

* Annual rhythms that are entrained by seasonal variations in daylength are called _____________

Answer 82

Annual rhythms that are entrained by seasonal variations in day length are called "photoperiodic rhythms." These rhythms rely on changes in daylight duration to regulate seasonal behaviors or physiological changes in organisms across the year.

Question 83

* Annual rhythms that persist for 2 or more years in constant conditions are called _____________

Answer 83

Annual rhythms that persist for 2 or more years in constant conditions are called "circannual rhythms." These rhythms continue over multiple years even when the external environment remains constant, resembling a longer-term internal calendar within the organism.

Question 84

* Is Seasonal Affective Disorder (SAD) in humans homologous with photoperiodism in mammals? Can SAD be controlled using melatonin?

Answer 84

Seasonal Affective Disorder (SAD) in humans shares similarities with photoperiodism in mammals, as both involve mood or behavioral changes in response to seasonal variations in light. However, they're not entirely the same. While SAD is linked to changes in daylight and affects mood, photoperiodism in mammals encompasses broader seasonal behaviors. Melatonin supplements are sometimes used to treat SAD because they can help regulate sleep patterns affected by changes in daylight. However, their effectiveness can vary among individuals, and other treatments or lifestyle changes might also be recommended for managing SAD.

Question 85

* Which parameter(s) of light determine(s) its efficacy as a treatment for SAD?

Answer 85

The effectiveness of light therapy for Seasonal Affective Disorder (SAD) depends on the intensity (brightness) and timing of light exposure. The right intensity and timing of light exposure are crucial for it to effectively alleviate SAD symptoms

Question 86

Does an increase in the duration of nocturnal melatonin secretion inhibit or stimulate reproductive activity or does this depend on the species?

Answer 86

The effect of increased duration of nocturnal melatonin secretion on reproductive activity can vary depending on the species. In some species, prolonged melatonin secretion can inhibit reproductive activity, while in others, it might stimulate or have no significant effect on reproduction

Question 87

What is the difference between a longitudinal and a cross-sectional study design? The discovery of seasonal SAD in humans requires which type of study design?

Answer 87

a longitudinal study follows the same group of individuals over a long period to observe changes over time. In contrast, a cross-sectional study looks at different groups at a single point to compare them. Discovering seasonal SAD in humans would typically require a longitudinal study design because it involves observing changes in the same individuals' mood or behavior across different seasons over an extended period to establish a seasonal pattern.