sleep - unit 4

what is sleep

a naturally occurring altered state of consciousness described as the suspension of awareness of the external environment

what are the two categories of consciousness

1. normal waking consciousness

2. altered state of consciousness

what is sleep latency

the amount of time it takes you from being fully awake to sleeping

what are the two purposes of sleep

1. evolutionary theory

2. restorative (rest and restoration theory)

what is the evolutionary theory

• humans became motivated to sleep during night for survival as there was less risk of injury and predators

• energy could be conserved for periods of activity in the day

what happens during energy conservation

• less muscle tension

• lower heart rate, blood pressure, temperature

• slower respiration

what is the restorative theory

homeostasis of the body is disrupted when humans are awake and sleeping allows the energy levels that decline during wakefulness to be restored

what happens during physical restoration

• rebuilds/repairs cellular components and materials used for biological functions during waking

• most growth hormone is released during slow wave sleep

• helps clean the brain by flushing out waste products that are potentially neurotoxic to CNS

• important for memory consolidation, especially creating long term memory

what is the sleep-wake cycle

the recurring pattern of wakefulness and sleep that comprises of two distinct, independent and opposing systems

what are the two systems of the sleep-wake cycle

1. sleep drive (homeostatic process)

2. an alerting force (circadian process)

what happens during sleep drive

• adenosine is proposed to act as a homeostatic regulator of sleep

• the extracellular level of adenosine increases in the brain during prolonged wakefulness and decreases during the sleep-recovery period

what happens during the alert or wake system

• circadian rhythm controls the release of melatonin and cortisol

• biological clock is controlled by the suprachiasmatic nucleus which responds to light and dark signals

• approximates homeostasis in coordination with environmental cues

what is the role of melatonin in the sleep-wake cycle

• in the evening, melatonin levels rise and body temperature lowers

• stays elevated through the night, promoting sleep

• SCN suppresses melatonin production as long as our eyes perceive light

what is the role of cortisol in the sleep-wake cycle

• released in the morning when our body temperature increases

• increases alertness, causing us to wake up

what are the two categories of sleep

• rapid eye movement (REM)

• non-rapid eye movement (NREM)

how many cycles of sleep do we experience

4-6 cycles of sleep, lasting around 90 minutes each

what are the 4 stages of sleep

stage 1: NREM 1

stage 2: NREM 2

stage 3: NREM 3

stage 4: REM

what is the function of NREM

replenishing the body

what is the function of REM

replenishing the mind as it restores brain functions and consolidates memory

what are the characteristics of stage 1 - NREM 1

Sleep state: transitional period between wakefulness and sleep

Heart rate: decreased heart rate

Eye movement: eyes slow rolling movement, once asleep, eyes stop moving

Muscle tension: muscles relax

what is the length of stage 1 - NREM 1

1-7 minutes

what are the characteristics of stage 2 - NREM 2

Sleep state: light non-REM sleep

Heart rate: starts to slow down

Eye movement: eye movement stops

Muscle tension: continue to relax and occasional muscle twitches

what is the length of stage 2 - NREM 2

10-25 minutes, increasing with each repetition

what are the characteristics of stage 3 - NREM 3

Sleep state: deep non-REM sleep

Heart rate: continues to decrease

Eye movement: minimal eye movement

Muscle tension: muscles are at their most relaxed

what is the length of stage 3 - NREM 3

20-40 minutes, but reduces in length to nothing

what are the characteristics of stage 4 - REM

Sleep state: dreams occur during this stage

Heart rate: generally increases to match the rate when awake, varies depending on dream content

Eye movement: rapid eye movement, visual info isn’t transmitted to the brain

Muscle tension: temporarily paralysed (atonia) except for breathing and eye muscles

what is the length of stage 4 - REM

10-60 minutes, increases in duration over the night

what is sleep deprivation

a condition characterised by inadequate or insufficient sleep

what are the causes of sleep deprivation

• shift work

• drugs

• sleep environment

• stressors

how does shift work cause sleep deprivation

• shift work alters the sleep-wake cycle and reduces the quality and amount of sleep

• people who work night shifts may have trouble sleeping during the day because exposure to light at night and dark during the day affects the circadian rhythm

how do drugs cause sleep deprivation

• caffeine is a stimulant drug that increases activity in the CNS, making it longer to get to sleep and less time in deep sleep

• alcohol is a depressant drug that can disrupt sleep when it wears off and raises the arousal threshold

how does sleep environment cause sleep deprivation

• being in brightly lit environments at night reduces levels of melatonin

• blue light also reduces the production of melatonin

how do stressors cause sleep deprivation

marital or family difficulties, problems at school or work and illness can make it more difficult to fall asleep and stay asleep due to anxiety

what is partial sleep deprivation

the severe reduction or complete lack of sleep over a short period of time

what are the effects of partial sleep deprivation

• attention

• mood

• reflex speed

• vision

how does partial sleep deprivation affect attention

lapses in attention increase when sleep deprived

how does partial sleep deprivation affect mood

can decrease mood and cause irritability in people

how does partial sleep deprivation affect reflex speed

reaction times tend to become higher meaning it takes longer to react to stimuli

how does partial sleep deprivation affect vision

can become blurry, eye twitches may occur and eyes may become more sensitive to light

what is chronic sleep deprivation

the persistent reduction of sleep over a long period of time at least 3 months

what are the causes of chronic sleep deprivation

sleep disorders such as insomnia or continual disturbances due to long work hours or lifestyle choices

what are the effects of chronic sleep deprivation

• heart disease

• obesity

• insomnia

• anxiety

how does chronic sleep deprivation cause heart disease

increased blood pressure and high cholesterol levels, both of which can lead to heart disease

how does chronic sleep deprivation cause obesity

increasing intake of high energy foods and drinks, overall the amount of food they eat

how does chronic sleep deprivation cause insomnia

characterised by difficulties falling asleep or staying asleep (low sleep latency) and wake up not feeling rested

how does chronic sleep deprivation cause anxiety

emotional regulation is negative affected by chronic sleep deprivation and can exacerbate symptoms of anxiety

what is sleep hygiene

the behaviour and sleep environment that result in achieving the quantity and quality of sleep required for good mental health and wellbeing

what are techniques to improve sleep hygiene

• management of electronic devices

• consistent sleep patterns

• creation of a healthy sleep environment

how does management of electronic devices improve sleep hygiene

• sunlight is the main source of blue light and exposure provides SCN the signal to keep us alert and increases cortisol

• blue light inhibits melatonin production which disrupts the circadian rhythm, making it hard to fall asleep

• emitted through LED lighting such as electronic screens

• to maintain the sleep-wake cycle, it is recommended to stop looking at screens at least 1-2 hours before bed

how does consistent sleep patterns improve sleep hygiene

• having a consistent sleep pattern is critical as it aids in regulating the circadian rhythm

• can increase amount of sleep and duration of sleep, preventing sleep deprivation

• done by setting the same bedtime and wake up time recommended for your age

how does creation of a healthy sleep environment improve sleep hygiene

• bedroom should be free of distractions, including electronic devices and be of a suitable temperature

• we shouldn’t eat for a few hours before bedtime to promote sleep

• the bed should be used for sleep or intimacy only, helping create a cognitive link between the bed and sleep