Sleep: Purpose and Characteristics Flashcards
Definition of sleep`
A necessity that is essential to being healthy, alert and happy, however the purpose of sleep is still debated
Evolutionary (circadian) theory of sleep
Sleep is an evolutionary response that adapts based on:
- the demands of how much food we need
- our energy requirements
- our safety when we sleep.
Proof of Evolutionary Theory
- There is a sequential pattern that demonstrates that the energy requirements of animals and number of predators correlate with sleep requirements. Sleep conserves energy
- Hibernation is important when food is scarce in Winter months.
Components of Evolutionary Sleep Theory
- Sleep demands on an animal’s vulnerability to predators
- Sleep depends on the need to find food
- Sleep conserves energy
Sleep demands on an animal’s vulnerability to predators
- Small animals that are very vulnerable to predators, such as mice, sleep more so they can hide safely from carnivores
- Larger prey animals, such as deer, sleep less because they are more exposed in their environment and need to be ready to escape from predators
- Those with few natural predators, such as bears, can sleep for up to 12-15 hours a day.
Sleep depends on the need to find food
- Animals that need to graze for hours, such as cows, sleep less
- They sleep less because they need to find more food to survive
Sleep conserves energy
- When an animal sleeps, its metabolism slows, thus reducing the need for food
- A human’s metabolic rate during sleep is about 10% less than when awake
Evolutionary Theory Criticisms
- Does not explain why we must have sleep
- All species sleep, despite the amount of food or danger they are in a way to hide safely from predators
- For animals that are highly preyed upon, sleeping can be dangerous
- Loss of awareness during sleep makes animals very vulnerable to predators
Restorative theory of sleep = rest and recover
Sleep replenishes our bodies and allows us to recharge depleted energy resources
REM replenishes the mind, NREM replenishes the body
Homeostasis is disrupted when humans are awake - sleep restores this
Sleeping allows energy levels during wakefulness to be restored
Restorative sleep functioning
Sleep:
- Repairs and replenishes the body and prepares it for action the next day
- Keeps minds alert and assists psychological state
- Activates hormones and neurotransmitters that can enhance mood
- Activates personal growth, especially during NREM3 and 4
Restorative Theory Criticisms
- Sleep activates growth, increases immunity and cognitive decline occurs with sleep deprivation
However, there is no supportive evidence that we need more sleep when we exercise. There is no evidence to support that people that do minimal exercise would sleep less.
Sleep-Wake Cycle
The recurring pattern of wakefulness and sleep that individuals undergo daily.
Measured through recording times of regular events (eating, going to sleep)
Circadian Rhythm
Bodily cycle that lasts around 24 hours and controls nocturnal release of hormones including melatonin
Function of Circadian Rhythm
- Body clock located in suprachiasmatic nucleus (SCN), a pair of distinct groups of cells in the hypothalamus
- Controls melatonin (hormone that makes you sleepy) through receiving information about incoming light from eyes
- When there is less light, SCN tells brain to make more melatonin so you get drowsy and can fall asleep
What regulates the sleep wake cycle?
- Circadian Rhythm
- Body temperature
- Metabolic rate
- Hormones like melatonin
Sleep hygiene
Behaviour and sleep environment that results in healthy sleep
Techniques to improve sleep hygiene
- Restricting electronic device usage at least one hour before bedtime
Blue light emitted from electronic devices inhibits melatonin production, stimulates the brain and disrupts circadian rhythm
- Consistent sleep patterns, which aids in regulating circadian rhythm
- Creation of healthy sleep environment; cognitive link between bed and sleep
Components of Sleep Wake Cycle
Three stages of NREM, one stage of REM
Night’s sleep is approximately 4 to 6 sleep cycles
Approximately 90 minutes per sleep cycle
NREM1
- Transitional period between wakefulness and sleep
- 1-7 minutes
- Heart rate decreased, muscles relaxed
- Eye movement slowed, stops when asleep
- If uninterrupted, moves to NREM2 (minimal time spent)
NREM2
- Light nonREM sleep
- Eye movement stops, muscles continue to relax with occasional twitches
- 20-40 minutes
- Heart rate starts to slow
- Repeated 10-25 minutes, increasing in length with each repetition
NREM3 / 4
- Deep nonREM sleep
- Minimal eye movement, muscles at their most relaxed
- 20-40 minutes
- Heart rate continues to decrease
- Repeated first few sleep cycles
REM
- Dreams occur during this stage
- Rapid eye movement, visual information not transmitted to brain
- 10-60 minutes
- Temporarily paralysed (atonia) except for eye and breathing muscles
- Increases to match rate when awake, varies with dream content
- Repetitions increase in duration over the night (few minutes to an hour)
Sleep Deprivation
The condition of not getting sufficient sleep.
- Characterised by inadequate or insufficient sleep sustained over a period of time
Sleep Latency
The time it takes to fall asleep.
Causes of sleep deprivation
Shift work
Drugs
Sleep environment
Stressors
Shift work
Alters hormones such as hormones that regulate the sleep-wake cycle (make us awake in day and feel tired at night)
Reduces quality and amount of sleep
Exposure to light at night affect circadian rhythms and affects ability to sleep during the day
Drugs
Impacts sleep stage progression (reducing amount of NREM or affecting REM sleep)
Caffeine is a stimulant drug that increases CNS activity
Alcohol is a depressant that disrupts sleep when it wears off, causing people to wake
Sleep environment
Being in brightly lit environments at night may reduce levels of melatonin, disrupting sleep-wake cycle
Environmental noise can decrease intensity of sleep
Stressors
Stressors (marital or family difficulties, work problems, illness etc) impact sleep routines and result in less sleep overall.
Partial (acute) sleep deprivation
Severe reduction or complete lack of sleep over a short period of time (24 hours or over a few consecutive nights)
Causes may include jetlag and other stressors
Effects of partial sleep deprivation
- Lapse in attention increase
- Decreases mood (irritability)
- Higher reaction time
- Eye spasms, more sensitive to light
Chronic sleep deprivation
Persistent reduction of sleep over a long period of time (more than a few weeks at a time, sometimes lasting for years)
Causes include sleep disorders (insomnia), long work hours, continued sleep disturbances
Outcomes are more difficult to reverse
Effects of chronic sleep deprivation
- Increased blood pressure and high cholesterol levels (can lead to heart disease)
- Increased intake and amount of high energy foods (obesity)
- Insomnia: Difficulty falling and staying asleep
- Anxiety: Emotional regulation affected, exacerbates symptoms of anxiety
