Chapter 10 - Sleep Flashcards
Body rhythms are endogenous cycles. What does the term “endogenous cycles” mean?
They are processes in your body that fluctuate over time. Exogenous (external) factors affect these rhythms
Cirannual cycles refer to ________.
Provide an example of a cirannual cycle.
Yearly cycles. Birds’ migratory patterns or animals storing food for winter.
Circadian cycles refer to _________.
Daily cycles.
Sleeping, eating, mood, body temperature.
Explain briefly how the eating circadian rhythm works.
We get hungry because of internally generated levels that signal to our body that we are hungry. This is not because we are low on blood glucose levels or that we are low in energy. Eating cycle can be trained.
List 4 traits associated with circadian rhythms.
1) They persist even in the absence of external cues.
2) They change with age.
3) They are adjusted by exogenous factors (external).
4) Sometimes, external factors are not fast enough at changing our circadian rhythms.
Provide an example of how circadian rhythms can persist even in the absence of external cues.
Hint: Flying squirrel
Flying squirrels were kept in constant darkness. Over time, their waking period started earlier each day than the last. This showed that their circadian cycle is less than 24 hours (as long as there are no external cues, such as the sun).
But, if external cues are present, they’ll adjust their internally generated cycles based on external cues and sleep roughly at the same time every day.
How do humans’ circadian rhythms change with age?
Adolescents are often night people, and young children are often morning people. As we get older, we become more morning people (although this depends primarily on genetics).
Measured time of the middle of sleep on days without obligations (weekend or holidays)
How are our sleep cycles adjusted by exogenous factors?
We re-adjust our internal cycles daily to stay in phase with the world. Eg: Taking in external cues like light to let us know when we are sleepy –> we get sleepy around the same time every day.
Why do more than half of all blind people report frequent sleep problems?
They cannot adjust their cycles their cycles using light.
Not all people are blind due to the same reason though! If blind person has problems in retina affecting vision, this can lead to problems with sleep because he/she cannot use signals in environment to adjust sleep. They can use other cues like sound or food but light is a more powerful cue.
Using an example, explain how sometimes external factors are not fast enough at changing our circadian cycles.
Eg: Jet Lag
Jet lag: Circadian rhythm tells you one thing (time to sleep!) but environmental cues tell you something else (it’s day time, you’re not supposed to be asleep!)
Over the course of a few days, your body starts adjusting to the new time schedule. Evolution did not prepare us for this, because we did not evolve in a situation where we could move thousands of km in a day.
Where is the suprachiasmatic nucleus located at?
It’s in the hypothalamus and lies just above the optic chiasm
- Supra means above.
Outline briefly the neural mechanism of sleep.
Photoreceptive RGC –> suprachiasmatic nucleus –>
Outline briefly the neural mechanism of sleep.
Photoreceptive RGC –> suprachiasmatic nucleus –> pineal gland
What happens when the photoreceptive retinal ganglion cells project to the suprachiasmatic nucleus?
1) The retina has photoreceptors which have ganglion cells that project to the brain. A small percentage of the RGS project specifically to suprachiasmatic nucleus.
2) These RGCs are more sensitive to short-wavelength (blue) light. These RGCs are photoreceptive (ie they have photopigments called melanopsin). They are the only ganglion cells in retina that that have photopigments. That means they respond to overall amount of light and not to instantaneous changes in light.
The SCN receives projections from special retinal ganglion cells: photoreceptive ganglion cells. Why do you think this is the case?
Because the SCN only cares about absolute levels of luminosity, so it does not need complex retinal processing
SCN only receives projections from special RGCs that are photoreceptive. This thus saves its time, as it can immediately sense light from the specific RGC.
What proteins promote sleep?
PER and TIM
What happens inside the Suprachiasmatic Nucleus (SCN)?
1) Genetic “clocks” inside SCN neurons: 2 proteins are generated by genes (PER and TIM)
- These 2 proteins either self-inhibit or inhibit each other: Mechanism is very complex
- Take 1 of these cells and put in a petri dish outside of brain. Cell activity will go up and down according to circadian cycle.
2) A few genes are expressed, hence creating mRNA. However, it takes some time for proteins to be created from these mRNA. After some delay, an increase in mRNA levels will lead to increased levels of proteins.
3) Transcription Factor: Proteins PER and TIM inhibit creation of themselves by inhibiting genes that produce them. Negative feedback loop: When there are high levels of these proteins, signals will be sent to the cell to stop producing. (more apt when it’s time for you to wake up)
4) Proteins PER and TIM promote sleep. Increase in proteins increases drive to sleep. (higher levels of PER and TIM when it’s time for you to sleep)
5) Light activates an enzyme that breaks down the TIM protein, thus adjusting the cycle (light = morning = wake up, that’s why at night the computer/phone light not very good).
- Light interacts with internally generated cycle, to manipulate when you will feel sleepy
- Breaks down TIM protein: problems falling asleep
6) Mutations in these genes cause sleep problems and depression.
Which part of the brain produces circadian rhythm?
What evidence is there to suggest this?
Suprachiasmatic nucleus
SCN cells isolated from the body continue to produce a circadian rhythm.
The SCN projects to ________, which produces _________.
Pineal gland, melatonin.
Pineal gland will receive activation from SCN, and will release melatonin as a result.
Describe briefly the production cycle of melatonin.
1) Melatonin production increases in the evening.
2) Melatonin levels peak in the middle of the night
3) Melatonin levels fall to normal daytime low by early morning
When does melatonin secretion start?
2-3 hours before bedtime.
List 5 interruptions of consciousness.
Sleep, coma, vegetative state, minimally conscious state and brain death.
What is sleep?
A state that the brain actively produces. Characterized by decreased response to stimuli
What is coma?
Extended period of unconsciousness caused by head trauma, stroke or disease. Characterized by low brain activity, low response to stimuli, no purposeful movements.
What is vegetative state?
Alternates between periods of sleep and low arousal. Characterized by low response to stimuli and no purposeful movements.
What is a minimally conscious state?
Like vegetative state, but with occasional brief periods of purposeful actions and limited amount of speech comprehension
Brain death refers to _________.
no brain activity.
What can be used to measure stages of sleep?
Polysomnograph - a combination of EEG and eye-movement records.
- Measures EEG signals (forehead and head)
- Measures eye muscle signal (beside eye)
- Reference electrodes (chin)
Describe the Fourier Transform method in translating frequencies in signals.
A method that translates this very complex signal into more digestible waves. Decomposes these signals into sinusoidal waves. If you add the waves together, it will recreate the original signals. Fourier shows that any continuous signal can be reconstructed using this method.
How are signals decomposed into sinusoidal waves?
Signals are decomposed into signals based on specific frequency and amplitude. Different frequencies will have different influences over the signals. Power of signal at specific frequency. Add points on dotted waves to get solid waves.
Describe alpha waves (2).
- 9-14Hz
2. Characteristic of relaxation, but not all of wakefulness.
What happens when one is relaxed and awake at the first stage of sleep? (3)
There will be high alpha waves at 9 - 12 Hz. High power in alpha band if decomposed using Fourier Transform
Not true for all awake states, only applicable to relaxed wakefulness.
What happens during Stage 1 of sleep? (3)
Irregular low-voltage waves. Brief moment before you fall asleep. Activity starts synchronising more (a bit).
What waves are present during Stage 2 of sleep? (2)
1) K- complex waves appear. They are big sharp waves associated with temporary inhibition of neuronal firing
2) Sleep spindle: High-frequency waves. Oscillatory interactions between cells in thalamus and cortex.
- 12-14Hz
Describe what happens during deep sleep (Stages 3 and 4).
Characteristic delta waves: Slow, high magnitudes delta oscillations. Low frequencies.
- Heart rate, breathing rate and brain activity decrease whereas slow, large-amplitude waves become more common.
- Stages 3 and 4 only differ in the prevalence of these slow waves.
- Some authorities combine it into slow-wave sleep aka these 2 into a single stage. Nevertheless, this indicates that neuronal activity in these stages is highly synchronized.
List some differences between Stage 1 + wakefulness and slow-wave sleep (3 and 4).
In stage 1 and wakefulness, the cortex receives much high-frequency output because most neurons are out of phase with one another. EEG is full of short, rapid and choppy waves.
In stages 3 and 4/ slow-wave sleep, sensory input to cerebral cortex is greatly reduced, and many cells can synchronize their activity.
Describe why REM sleep is also known as PARADOXICAL sleep.
Similarities to awake/light sleep: Increased neuronal activity + low voltage sleep (Stage 1)
Similarities to deep sleep: Postural muscles are more relaxed than in other sleep stages, body is completely blocked from moving except for eyes.
Paradoxical because there are similarities to light (awake) and deep sleep (muscle tone)
During deep non-REM sleep, there are large delta waves in the EEG signal. What can you deduce about processing and synchronization in the brain?
There is very little processing with large-scale synchronization.
- Recall: Large delta waves in deep sleep.
- Large fluctuations and large degrees of synchronization. Processing less information and there is less variability and heterogeneity in response
Contrast with awake state: Each cell is doing their own thing, so small fluctuations –> info will be very richly processed.
It is impossible to skip stages in sleep. True or false?
False. can skip.
When do deep sleep stages occur in the sleep cycle?
Occurs more commonly in early stages of the night (dominate in fact). Until 2 am in the morning, we have large density of deep sleep
When does REM sleep dominate the sleep cycle?
Towards the morning.
The longer you sleep, the more you will have big chunks of REM sleep at the end of the night. Dreams are more common during REM sleep, but also occur sometimes during non-REM sleep. But we know very little about sleep.
Define local sleep phenomenon.
The phenomenon that parts of the brain can take turns to sleep.
Which parts of the brain are responsible for making the body relaxed during REM sleep?
Pons and medulla.
How was the local sleep phenomenon experiment carried out?
In humans, parts of the brain can also fall asleep. Experiment was conducted such that subjects have electrodes that could measure local field potentials (EEG signals) and spiking activity of neurons - one electrode in the frontal love and another in parietal lobe.
What was found when some parts of the brain went to sleep?
Delta wave synchronization was observed when cells go quiet. Although 5-10% of the cells are synchronized, this proportion is large enough to see the synchronizations of delta waves.
When we are so tired that we need to sleep, what happens?
Ascending modulatory systems kick in, where GABA is released by nuclei in basal forebrain. Whole brain goes into sleep state.
What happens when you sleep without hitting Stages 3 and 4?
Wake up but feel tired even after a whole night of sleep
What happens when you don’t get REM sleep?
Feel rested, but if repeated over many nights, you might start hallucinating during your waking time.
What is sleep apnea?
A sleep disorder characterized by the inability to breathe while sleeping for a long period of time.
What are the long-term, chronic consequences of sleep apnea?
Sleepiness during the day
Impaired attention
Depression
Sometimes heart problems.
What are some causes of sleep apnea and how to treat it?
Genetics, hormones, old age, obesity, deterioration of the brain mechanisms that control breathing.
Give patient a mask that forces oxygen into their airways
What is narcolepsy?
A neurological disorder due to loss of neurons that produces orexin
_________ keeps you awake. _________ produces it.
orexin. hypothalamus
so it means that you will always feel sleepy
________ increases wakefulness and it’s produced by the __________
Norepinephrine, locus coeruleus
What are some main symptoms of narcolepsy?
- Attack of sleepiness during the day
- Occasional cataplexy (attack of muscle weakness while person is awake - often triggered by strong emotions)
- Sleep paralysis (inability to move while falling asleep or waking up). but can be experienced by healthy individuals but those with this condition experience it more often.
- Hypnagogic hallucinations: dreamlike experiences that person has trouble distinguishing from reality.
What is sleepwalking?
Parts of brain are awake while some are asleep, and person walks during sleep. most common during sleepless SWS and not during REM where most large muscles are completely paralyzed
Sleep is a passive process. True or false?
False. It is active because we do have mechanisms that force us to sleep.
List how memory replay in sleep helps to consolidate memories.
Use rodent studies to explain.
Measured cells in the hippocampus learning to explore environment.
Found that there is a chronological sequence of activation while animal is learning. Found the same sequence of activation when animal is sleeping. Could mean that the animal may be rehearsing what happened during the learning experience in its sleep.
What about the memory replay hypothesis makes it a less dominant explanation in explaining memory consolidation in sleep?
Postulated that forward and reverse replay can occur during sleep. however, replay also does occur during the awake period.
Still ongoing research. not so relevant for learning, but rather there are sequences that occur no matter what.
How does synaptic downscaling help in consolidating memories?
Recall: LTP refers to the strengthening of connections between cells when we learn something. If we keep learning, our brains will eventually explode with super powerful connections.
At night, synaptic downscaling is a mechanism that takes place, so that we don’t explode with the strengthening of connections in the brain. Everyday: Average decrease in activity = increase in activity. Size of synapses on average will grow to be much larger after sleep. Enough to maintain our brain is a balance. Decreases synaptic size after sleep - occurs primarily in weak synapses (sparing larger ones)
Explain how sleep spindles help in consolidation of memories.
High-frequency fluctuations during Stage 2 sleep. Sleep spindles increase after learning.
Non-REM sleep stays more or less stable while REM sleep increases over time? True or false (both)?
true, false
REM decreases over time.
Is it known why we have REM sleep? What are the hypotheses for it?
No we don’t know.
How is REM sleep suspected to help in memory consolidation? What is being disputed about this?
Characteristic of sleep: Depriving first half of sleep impairs verbal learning and depriving second half impairs motor learning. REM occurs in 2nd half so would no REM sleep impair motor learning?
Nope because people taking antidepressants (which significantly decreases REM sleep) have no memory problems.
How does REM sleep help in shaking of eyeballs? WHat is being disputed about this?
Our corneas receive oxygen from the air and a liquid that surrounds it. It is possible that REM sleep’s function is to move the eyes to shake the liquid and permit oxygen to reach the cornea. But people taking antidepressants (which significantly decreases REM sleep) have no damage to corneas.
