sleep

Question 1

how do we measure brain activity during sleep?

Answer 1

by attaching electrodes to the scalp to record an electroencephalogram (EEG)

Question 2

how do we measure muscle activity during sleep?

Answer 2

by attaching electrodes to the chin to record an electromyogram (EMG)

Question 3

how do we measure eye movements during sleep?

Answer 3

by attaching electrodes by the eyes to record en electro-oculogram (EOG)

Question 4

is it hard to wake up during deep sleep?

Answer 4

yes

Question 5

describe muscle tension during sleep stages

Answer 5

stage 1 to 3: muscles are not moving, but there is muscle tension. the muscles are at rest but not totally relaxed
REM: all muscle entirely relax (no movements on the EMG)

Question 6

describe eye movements through sleep stages

Answer 6

from stage 1 to 2 the eyes calm down.
stage 3: a bit of eye movements
REM: eyes moving a lot

Question 7

descrie beta activity

Answer 7

13-30 Hz; typical of an aroused state.
the high frequency, low amplitude oscillations relfect desynchronous neural activity

Question 8

describe alpha activity

Answer 8

8-13 Hz; typical of awake person in a relaxed state

Question 9

describe theta activity

Answer 9

4-8 Hz; appears intermittently when people are drowsy, and is prominent during early stages of sleep

Question 10

describe delta activity

Answer 10

<4 Hz; occurs during deepest stages of slow-wave sleep. the low frequency, large amplitude oscillations reflects synchronized neural activity

Question 11

describe Rapide eye movement sleep (REM)

Answer 11

it’s associated with dreaming, rapid eye movements, desynchronized neural activity and muscle paralysis. cerebral blood flow and oxygen consumption increase, but muscles are totally inactive apart from occasional twitches.

Question 12

describe deep sleep

Answer 12

non-REM sleep stage 3/4 is called deep, slow-wave sleep. it is associated with low frequency, large amplitude EEG signals.

this pattern of EEG activity bursts of action potentials in large groups of cortical neurons

Question 13

describe REM deprivation studies conclusion

Answer 13

we don’t know what REM is for

Question 14

describe the experiment that led us to know lack of sleep causes death

Answer 14

an experimental rat is kept awake by movements of the cage floor, which are triggered whenever their EEG suggests the onset of sleep. The EEF of a neighboring “control” rat does not trigger movements of the floor, so they can get some sleep.
after a few weeks in this chamber, the experimental rat will lose control of their metabolic processes and body temperature. they tend to lost body weight before they die, despite eating lots of food.

Question 15

what happens when you don’t sleep?

Answer 15

-mind begins to deteriorate, even though body is physically fine
-exhibit delayed reaction times and poor judgment as measured on cognitive tests
-increases in stress hormones, mood swings and impulsive behavior
-worse learning and memory
-intermittent sleep deprivation -> weight gain, but severe sleep deprivation -> weight loss, migraines, hallucinations, dementia, seizures, death
-sleep debt is created
-microsleep states often appear, animals fall asleep for brief periods lasting several seconds, during which time they are perceptually blind. people are often unaware of the occurence of these microsleep states
-sleep disruptions often precede and exacerbate mental illnesses

Question 16

how do dolphins sleep?

Answer 16

the two cerebral hemispheres take turns. only one hemisphere sleeps at a time.
we don’t know if they have REM sleep.

Question 17

describe the developmental differences between species.

Answer 17

large within species:
newborn human -> 16 hours (50% REM)
adult humans -> 7 hours (25% REM)

even larger between species:
-total amount of sleep per day
-proportion of REM to non-REM sleep
-length of sleep cycles (average time between periods of REM)

Question 18

true or false: predatory animals indulge in short interrupted periods of sleep.

Answer 18

false: predatory animals indulge in long, uninterrupted periods of sleep.

In contrast, animals that are preyed upon tend to sleep in short intervals lasting only a few minutes.

Question 19

what is the correlation between sleep and body weight?

Answer 19

the amount of time a species sleeps each day in inversely correlated with body weight.

Question 20

what is the correlation between metabolic rate and body weight?

Answer 20

across species, basal metabolic rate (BMR) increases proportionally with body mass; the more massive a species is, the more calories they burn while at rest.

Yet, larger species have a lower basal metabolic rate per cell (per pound). each cell requires less energy overall. Across species, larger animals have lower metabolic rates per cell and longer lifespans.
They don’t sleep very much overall, but each sleep session is relatively long.

↑ body mass, ↑ brain mass, ↑ overall metabolic rate, ↓ metabolic rate per cell, ↑ life span, ↓ heart rate, ↓ total sleep time, ↑ length of sleep cycles

Question 21

explain the hypothesis that correlations relate to the efficiencies of being large and the inefficiencies of being small.

Answer 21

Large animals benefit from economies of scale
(i.e. heat savings and more efficient nutrient & waste distribution networks), so each cell doesn’t have to work as hard as in a small animal.

The fact that total sleep time is correlated with these other variables suggests that sleep may be critical for a restorative process that benefits from economies of scale.

Question 22

describe the waste-removal hypothesis to answer the question: why do animals sleep?

Answer 22

The concentration of some cellular waste (extracellular proteins) increases in the brain across periods of wakefulness and decreases during sleep. Sleep could be required for efficient waste removal, as some evidence suggests that diffusion in the brain and the clearance of waste products increases during sleep. Some glial cells (astrocytes) may expel water and shrink in size during sleep, increasing the volume and rate of diffusion of the cerebrospinal fluid, which would clear away waste. Larger brains may have more space to accumulate waste, and they might be able to clear waste away faster than smaller brains.

Question 23

does what we do during the day affect how much we sleep?

Answer 23

No. The amount of sleep we get does not correlate with what we do during the day, how much we exercise, or how much we study.

When people start an exercise program (or suddenly get confined to a wheelchair), they typically do not sleep any more or less than normal.

The caloric difference between a person sleeping and sitting still over 8 hours is negligible
(~110 calories).

Hibernation is different. Hibernation is associated with an extreme slowdown of metabolic processes (to about 5% of normal) and reductions in heart rate, breathing, and body temperature, which all dramatically reduce energy needs.

Question 24

What is the glymphatic system?

Answer 24

Cerebrospinal fluid (CSF) is continually made in brain ventricles. It circulates around and diffuses into the brain, becoming the extracellular solution that surrounds neurons. As CSF moves through the brain, it picks up waste products before exiting into the blood.

Question 25

why didn't animals simply evolve to have bigger brains?

Answer 25

The evolutionary pressure to control and constrain diffusion in the brain may have created a situation where waste products could not be effectively cleared while awake.

Question 26

Explain the ionic gradient rebalancing hypothesis to answer the question: why do animals sleep?

Answer 26

some people argue that the volume of extracellular space in the brain does not substantially change across sleep-wake transitions. But there may be a rebalancing of ionic gradients ((Na⁺, K⁺, Ca²⁺, Cl⁻, Mg²⁺, H⁺) to ensure optimal conditions for brain function. the capacity of the brain to buffer changes in ion concentrations and pH (the acid-base balance) may determine total sleep time and benefit from economies of scale.

Question 27

Describe the brain plasticity / learning & memory / synaptic homeostasis hypothesis to answer the question: why do animals sleep?

Answer 27

neural networks are constantly reorganizing as information is learned and forgotten. synapses grow stronger and weaker. new synapses form and old ones get eliminated. maybe the brain cannot safely or efficiently perform large updates on synaptic connections while it is awake and processing new information sleep could be an opportunity for the brain to reorganize information and archive memories. synaptic modifications clearly occur during sleep. and learning and memory are both impacted by sleep. some evidence suggests that the amount of slow-wave sleep correlates with improvements in procedural memory. the brain is clearly very active during sleep and doing something special.

Question 28

true or false: REM stages become longer and longer through the night.

Answer 28

true

Question 29

true or false: deep sleep stages becomes shorter and shorter through the night

Answer 29

true

Question 30

what is circadian rythm?

Answer 30

there are many changes in behaviour and physiology that follow a 24-hour cycle. animals adjust to shifts in the daily light cycle. for example, rats quickly adapt when the daily light cycle is shifted by a couple hours. circadian rhythms are controlled by internal biological clocks that continue to run in the absence of light.

Question 31

what happens with rats if light levels suddenly stop changing (complete darkness or constant dim light)?

Answer 31

rats largely maintain their circadian rhythms. without any external light cues, rats naturally maintain a rhythm between 23 and 25 hours.

Question 32

where is our circadian clock located?

Answer 32

in the suprachiasmatic nucleus (SCN) of the hypothalamus. this area gets direct input from the retinal ganglion cells.

Question 33

what happens when you lesion the SCN?

Answer 33

it does not change the total amount that animals sleep, but it dramatically alters their circadian rhythms (the length and timing of sleep-wake cycles and hormone secretions).

Question 34

true or false: in continuous dim light conditions (DD) brief pulses of bright can shift the internal circadian clock.

Answer 34

true

Question 35

how does the suprachiasmatic nucleus keep time in complete darkness?

Answer 35

The 24-hour clock in the SCN is largely maintained by two interlocking feedback loops. Basically, when the expression of one protein becomes high enough, it inhibits its own production and promotes the expression of a different protein. The genes involved in time keeping are the Period genes. Rare mutations in the Period genes can shift the circadian clock earlier or later.

Question 36

what is advanced sleep phase syndrome

Answer 36

it is caused by mutation in the Per2 gene. it produces a 4-hour advance in the circadian clock, leading to a strong desire to fall asleep at 7pm and wake up at 4am.

Question 37

what is delayed sleep phase syndrome?

Answer 37

it is caused by mutation in the Per3 gene. it produces a 4-hour delay in the circadian clock, leading to a strong desire to fall asleep at 2 am and wake up at 11 am.

Question 38

what determines how much sleep an animal needs? SCN lesions do not change total sleep time.

Answer 38

Consistent with the waste removal theory of sleep, there is a build-up of certain molecules in the extracellular fluid of the brain during waking hours. Some of these molecules promote sleep at high concentrations. The adenosine molecule (part of ATP) has received the most attention. Extracellular levels of adenosine rise during waking hours and accumulate even more with sleep deprivation. Adenosine levels fall rapidly in the brain during sleep, even during brief intrusions of sleep. Drowsiness and the duration and depth of sleep are strongly modulated by adenosine receptor signaling throughout the brain. Adenosine may be one of many sleep-inducing molecules in the brain. It is possible that the build-up of these molecules during waking hours underlies animals’ need for sleep.

Question 39

true or false: caffeine is an adenosine receptor agonist.

Answer 39

false, antagonist

Question 40

name the signalling molecules that are released during periods of arousal, alertness and wakefulness, and decrease during sleep.

Answer 40

serotonin, norepinephrine acetylcholine orexin histamine orexin and histamine are neuropeptides that are released by neurons in the hypothalamus. histamine receptor blockers (antihistamines) often cause drowsiness.

Question 41

true or false: norepinephrine release correlates with focus and attention.

Answer 41

true

Question 42

true or false: many drugs that increase serotonin signalling suppress certain aspects of REM sleep.

Answer 42

true

Question 43

true or false: serotonin and norepinephrine release decreases across the day and spikes as soon as you wake up.

Answer 43

true

Question 44

true or false: serotonin release correlates with arousal.

Answer 44

true.

Question 45

what is the ventrolateral preoptic area (vIPOA)?

Answer 45

one area of the hypothalamus that promotes sleep. -electrical stimulation of this region causes drowsiness and sometimes immediate sleep. lesions suppress sleep and cause insomnia. -vIPOA neurons inhibit wake-promoting neurons throughout the brain. And the vIPOA receives inhibitory inputs from the same regions it inhibits. -this kind of reciprocal inhibition characterizes a flip-flop circuit; both regions cannot be active at the same time, and the switch from one state to another is fast. -animals awaken when their arousal neurons are more active than their vIPOA neurons. animals sleep when their vIPOA neurons are more active than their arousal neurons.

Question 46

what is the sleep molecule hypothesis (adenosine version)

Answer 46

-extracellular adenosine levels build-up during the day. -at high concentrations, adenosine stimulates sleep-promoting vIPOA neurons and inhibits the arousal-promoting acetylcholine (ACh) neurons. -brain transitions in or out of sleep when the activity of the clock neurons in the SCN aligns with the build-up (or clearance) of sleep-promoting molecules.

Question 47

what is orexin

Answer 47

a peptide produced by neurons in the lateral hypothalamus. these neurons promote wakefulness and their activity increases when there are reasons to stay awake. most forms of narcolepsy are associated with the absence of orexin neurons. Orexin neurons clearly promote arousal, but they also prevent the emergence of REM sleep components in the waking state.

Question 48

what is narcolepsy?

Answer 48

rare sleep disorder -characterized by periods of excessive daytime sleepiness and irresistible urges to sleep. -associated with the death of orexin neurons in the hypothalamus. They seem to be attacked by the person’s own immune system, usually during adolescence or young adulthood.

Question 49

what is sleep paralysis?

Answer 49

symptoms that can occur on their own or with narcolepsy when REM-associated paralysis occurs just before a person falls asleep or just after they wake up. It is often accompanied by vivid, dream-like hallucinations.

Question 50

what is cataplexy?

Answer 50

symptoms that can occur on their own or with narcolepsy when a person experiences complete muscle paralysis while awake. It is typically triggered by a strong emotional reaction or sudden physical effort (e.g., laughter, anger, excitability).

Question 51

what is insomnia?

Answer 51

difficulty falling asleep or after awakening during the night It is a problem that affects ~25 percent of population occasionally and 9 percent regularly.

Question 52

what is fatal familial insomnia & sporadic fatal insomnia?

Answer 52

rare diseases that involve progressively worsening insomnia, which leads to hallucinations, delirium, confusional states, and death within a few years. fatal insomnia is associated with progressive neurodegeneration around the thalamus, hypothalamus, and/or brain stem.

Question 53

name some non-REM parasomnias and describe them.

Answer 53

Sleepwalking, Sleep-talking, Sleep-groaning, Sleep-crying, Sleep-eating, Sleep-masturbating, Sleep-teeth grinding These behaviours tend to occur in the first half the night, and people are often unaware that they do them. Episodes can last seconds to minutes or longer, as the brain is caught in a state between sleeping and waking. Some non-REM parasomnias are more prevalent in children. People often grow out of them. But some medications and medical conditions can trigger non-REM parasomnias.

Question 54

what are sleep terrors?

Answer 54

disorder of non-REM sleep. -waking with an overwhelming feeling of terror, which can include panic, screaming, and bodily harm caused by rash actions. Sleep terrors are common between the ages of 3 and 7 years, and kids often have no recollection of these events. Sleep terrors are not common in adulthood, but they frequently occur with PTSD.

Question 55

what is the only sleep disorder associated with REM sleep?

Answer 55

REM sleep behavior disorder, in which a person does not become paralyzed during REM sleep and thus acts out their dreams. This disorder often occurs prior to Parkinson's disease, although not everyone with Parkinson’s disease experiences it.