Sleep Flashcards
(38 cards)
Define sleep and the two theories that explain the purpose of sleep
Regularly occurring, altered state of consciousness where awareness of the external environment is suspended, with characteristic physiological changes
-> Evolutionary Theory
-> Restorative Theory
Explain the Evolutionary (circadian) theory of sleep and its factors
Evolutionary (circadian) theory of sleep describes sleep as a means of increasing the organism’s chance of survival in its environment by changing to meet the demands of its environment.
-> Energy conservation- organisms experience less muscle tension and lower heart rate, body temperature, blood pressure and breathing rate when asleep to conserve energy
-> Niche adaptation- organisms have adapted their sleep patterns to their environmental conditions (niche) to aid in survival via natural selection
Explain the Restorative theory of sleep and its factors
Restorative theory of sleep posits that sleep enables us to grow, repair and replenish the body (physical and psychological) after the work done when awake
-> Physical restoration: Occurs in NREM, body releases most growth hormone when in deep sleep, waste products are removed (e.g., the neurotransmitter adenosine, which accumulates when we release energy during wakefulness), mood hormones and neurotransmitters are activated during sleep (hence grumpiness when sleep is lacking), immune cells are produced (hence getting sick when lacking sleep), and various proteins used are replenished
-> Mental restoration:
REM sleep is thought to help renew mental processes (brain is quite active during this phase of sleep, and it may be during this time that the brain ‘exercises’ neuronal connections in order to keep brain circuits functioning)
-> Memory consolidation:
REM and deep sleep seem to be important in memory consolidation
- Sleep helps us to remember what we have learned due to its role in consolidating memories (different types of memories are thought to be processed during different stages of sleep - declarative memory during deep sleep and procedural memory during REM sleep)
What are the criticisms given to the Evolutionary and Restorative Theories of sleep
-> Evolutionary theory of sleep doesn’t explain why sleep is so essential (for instance, we still sleep even though we are unlikely to be in danger):
-> Sleep may make some species more vulnerable to predators (e.g., small animals)
-> Restoration theory of sleep assumes sleep is related to activity but this doesn’t hold true (e.g., bed-bound people do not sleep less);
Explain what is the Sleep-Wake Cycle
The sleep-wake cycle is a process where an organism alternates between sleep and wakefulness
-> In humans, the hypothalamus contains an internal ‘clock’ called the suprachiasmatic nucleus, which sets our sleep-wake cycle as well as body temperature cycle and growth hormone secretion in a circadian rhythm (a pattern of changes which occurs about every 24 hours)
- There are also infradian rhythms (more than 24 hours, such as menstruation) and ultradian rhythms (less than 24 hours, such as sleep stages)
-> In humans, hormones such as cortisol (made by the adrenal glands and linked to alertness) and melatonin (made by the pineal gland and released during darkness, causing sleepiness) are regulated by the suprachiasmatic nucleus
-> Cyclical changes in levels of these hormones result in the pattern of sleepiness and wakefulness
How long is the Humans sleep cycle and what effect does it have?
Human sleep cycles run on approximately 24.2 to 25 hour cycles - hence we often don’t feel sleepy when it is ‘bedtime’, according to the clock!
-> Since this is slightly different to the 24-hour time system, if we followed our natural sleep pattern, we would quickly fall out of pace with natural daylight and night times
-> This mismatch is adjusted for by the effect of external cues called zeitgebers (mainly light) on the suprachiasmatic nucleus, which signals the pineal gland to stop releasing melatonin and hence stop making us sleep
What are the different Sleep Stages?
-> Non-rapid eye movement sleep (NREM)
-> Rapid eye movement sleep (REM)
Explain NREM Sleep
NREM- 80% of the time, mostly without dreaming, 3 or 4 stages. each progressively deeper
-> Electrical activity of the brain, heart rate and breathing slows and secretion of some hormones increases (e.g., growth hormones)
-> Tend to experience more NREM sleep if recovering from physical exertion
Explain REM Sleep
REM- 20% of the time, experience most dreams
-> This has been implicated in memory and learning; increases after emotionally charged events (evidence shows that dreams are helpful in processing emotions and organising memories)
-> Time for REM increases and NREM decreases as night progresses hence dreaming right before waking
Explain the aspect of sleep cycles
-> A typical sleep cycle last from 90 to 110 minutes
-> 4 to 5 cycles occur per night but propotion of time spent in stages varies, with time spent in NREM sleep decreaing (which may be skipped entirely at the end) and time spent in REM sleep increasing (about an hour in the final cycle)
-> Sleep cycles can be plotted on a hypnogram
- First cycle- N1, N2. N3, N4, N3, N2, REM
- Second cycle: often skip N1 and go straight back into N2, N3, N4, N3, N2, REM (longer)
- Third cycle: often miss stages 3 and 4; again, REM is longer; later cycles (4,5 and possibly 6) are similar
-> We may wake briefly before or after REM sleep, but return to sleep
-> The pattern may vary from person to person (and night to night), but the features indicated next are the same)
Define Sleep Deprivation, What are the different types and what are the causes for sleep deprivation
Sleep deprivation- defined as not getting the sleep needed, or sleep of poor quality
-> It can be either partial or chronic
-> Causes include:
- Shift work
- Drugs
- Sleep environment
- Stressors
Explain the cause called Shift work of Sleep Deprivation
Shift work requires a person to work outside of normal working hours or rotate the schedule between these and typical working hours also
-> Shift work often requires alterations to the sleep-wake cycle, which decreases both quantity and quality of sleep
-> Particularly, problematic are night shifts because it opposes our natural circadian rhythm
which can lead to chronic sleep disturbances, and if the person cannot adjust, most commonly leads to circadian phase disorders (where the internal circadian rhythm is disrupted by exposure to light and dark at unnatural times, leading to daytime sleepiness)
- E.g., exposure of the night-shift worker to daylight (zeitgebers) decreases melatonin production, causing wakefulness when trying to sleep
-> Shift work sleep disorder (specific circadian disorder) - characterised by fatigue when awake and insomnia when trying to sleep leads to deadly fatigue-related mistakes and accidents (truck drivers)
-> Companies need to monitor the wellbeing of these employees, rotate rosters (forward and backward) and provide longer breaks when adjusted to new work hours
Explain the cause of drugs on Sleep Deprivation
Drugs are therapeutic and illegal substance that alter our normal physical and/ or psychological functioning which can then as a result interfere with sleep, causing insomnia (a sleep disorder marked by a long-term inability to fall asleep and/or stay asleep)
-> Sleep problems associated with common therapeutic medications may result from side effects of the medications (restlessness) which then promotes waking and also decreases melatonin levels, changing REM sleep time and altering the Sleep Wake Cycle
-> Caffeine (negative effect on sleep) is a stimulant (increases activity of the CNS) which then interferes with sleep (coffee, tea)
-> Alcohol (negative effect on sleep) is a depressant (decreases activity of the CNS) which initially may increase sleepiness, but then disrupts sleep as it wears off, causing the user to wake
-> With drawl from the drugs tends to increase difficulty with sleep which can drive the individual to resort back to substance use in order to obtain sleep or drug reliance to sleep from people with sleep disorders (dependence)
Explain the cause of unsuitable sleep environments on Sleep Deprivation
Unsuitable sleep environment may also result in interrupted, delayed or poor quality sleep
-> Temperature should be around 18 to 20 degrees for optimal sleep
- cyclical decrease in body temperature is a signal for sleep to occur
- When temperature is too high (or too low), falling asleep and maintaining sleep may be difficult
-> Noise has a strong negative impact on sleep (both inside and outside), as it fragments sleep when loud enough (decreases sleep intensity), causes waking
- Alters sleep cycle; more time in N1 and less in N3/N4 and REM sleep
-> Light, light exposure suppressing melatonin release in sleep wake cycle (most sensitive to this effect an hour after waking, two hours before sleep and at night)
- Exposure to significant artificial light during the evening, this can delay the internal ‘clock’, reducing melatonin and making it more difficult to sleep and resulting in more fragmented sleep
Explain the cause of stressors on Sleep Deprivation
Stressors are anything which promotes stress (feeling of emotional and/ or physical tension which results from an individual’s response to a stressor)
-> It activates the sympathetic nervous system, which prepares the body for action hence increases secretion of adrenaline and cortisol and increased heart and breathing rate occur, among other changes are associated with wakefulness
-> Thus the combination of delayed sleep (due to worry) and fragmented sleep (due to fight or flight response) results in sleep deprivation which may result in greater irritability and impaired function during wakefulness, which further contributes to stress
-> Sleep reactivity is defined as the degree to which a given amount of stress disrupts the sleep cycle, and may have a genetic component
Define Acute/ Partial Sleep Deprivation and state its Psychological effects
Partial sleep deprivation means getting partial sleep but not sufficient to meet needs for a 24 hour period or more, up to a few consecutive nights (less than 5 hours of sleep per night for a few consecutive nights)
-> E.g., pulling an ‘all-nighter’ to finish work is a short-term stressor
-> Psychological Effects:
- Mood
- Attention
- Reflex Speed
- Vision
Explain the Psychological effect of Mood on Partial Sleep Deprivation
Mood- affects our ability to recognise facial expressions of others, which impairs our emotional intelligence
-> The frontal lobe is particularly sensitive to sleep deprivation, and thus the ability to process emotions (both of self and others) and to respond appropriately is impaired hence emotional responses are amplified
-> May be due to a loss of REM sleep, as this is when release of neurotransmitters such as norepinephrine is interrupted, giving the receptors a ‘rest’
Explain the Psychological effect of Attention on Partial Sleep Deprivation
Attention- difficulty in maintaining attention, selective attention and dividing attention effectively and processing and remembering information (Negative affect)
-> Higher-order tasks (frontal lobe) and tasks requiring vigilance (long-term attention) are particularly impaired
-> Lapses in vigilance may be due to microsleeps (brief bursts of sleep-like EEG activity during waking) in response to fatigue
Explain the Psychological effect of Reflex Speed on Partial Sleep Deprivation
Reflex speed- difficulty in maintaining selective attention and switching being tasks
-> Microsleeps related to fatigue, impair performance which can increase reaction times (particularly dangerous when carrying out tasks requiring rapid responses to avoid danger, e.g., operating heavy machinery)
-> Sleep inertia- that woozy, dopey feeling we feel on wakening from insufficient sleep (especially in 3/4 NREM sleep) which can lead to accidents occurring
Explain the Psychological effect of Vision on Partial Sleep Deprivation
Vision- impaired, as they eyes require at least 5 hours’ rest for adequate recovery (minimum)
-> After sleep deprivation, there is often difficulty in focusing the eyes, blurred vision and increased eye twitching, due to the muscle controlling the eyes being exhausted
-> Eyes become more sensitive to light; dry eye also occurs due to reduced tear secretion
How can you recover from Partial Sleep Deprivation
-> Return to our normal sleep patterns can lead to recovery for few nights of poor sleep (fall asleep faster and for longer)
-> Sleep debt does not have to be ‘paid back’ hour for hour - a couple of hours of extra sleep over the next few nights will suffice
-> The major danger in acute partial sleep deprivation lies in accidents which may occur, and in the possibility of the sleep deprivation becoming chronic
Define Chronic Sleep Deprivation and the different Physiological Effects
Chronic sleep deprivation- getting inadequate sleep for more than a few weeks’ time
-> Effects of chronic sleep deprivation are often more severe than for partial sleep deprivation, and more difficult to reverse as considered a type of long term Sleep deprivation and can lead to sleep disorders such as insomnia
Physiological Effects:
- Insomnia
- Heart Disease
- Obesity
- Anxiety
Explain the Physiological effect of Insomnia on Chronic Sleep Deprivation
Insomnia- inability to sleep adequately regardless of opportunities to do so (sleep disrupted hence impairment in normal waking hours)
-> Causes (e.g., psychological/ health) are due to disruptions to the normal circadian rhythms, which if persistent, may then become a delayed sleep phase disorder (where the normal sleep-wake cycle is out of sync with the demands of society - usually falling asleep too late and waking too late)
-> Other common effects of insomnia include a decrease in the amount of quality of sleep, sleepiness, fatigue
Explain the Physiological effect of Heart Disease on Chronic Sleep Deprivation
Heart disease- during slow wave sleep, heart rate, breathing rate and blood pressure all decrease in the cardiovascular system and tend to stabilise, giving the heart the chance to repair and recover from daytime stresses
-> Poor sleep is also linked to an increase in inflammation, which causes buildup of plaques in the arteries (arteriosclerosis), increasing stroke risk
