sleep Flashcards
what is sleep?
a reversible, behavioural state of perceptual disengagement from and unresponsiveness to the environment
- involves a cyclical progression through different states associated with different levels of alertness and physiological responses
what are the 3 characteristics of sleep?
- reversibility: a sleeper can be awoken
- perceptual disengagement: lack of awareness of sensory stimulus in the external environment (which in a waking state you are aware of)
= therefore people are unresponsive
what is a biological rhythm?
cyclic changes in bodily functions that repeat themselves in the same order through time
eg. body temp, secretion of certain hormones, sleep-wake cycle
- controlled by internal mechanism - “biological clock” coordinated by the brain
what is the circadian rhythm and its characteristics?
cycle that involves changes in bodily functions or activities that occur ~ 24 hours duration (closer to 25 hours without external cues)
eg. sleep-wake cycle
describe the sleep-wake cycle
- sleepiness is highest at night= feel different levels of alertness at different times of the day
- internally produced and function in the absence of external cues
- but can be influenced by environmental time cues eg. clocks, meal times, noise, light
what are zeitgebers and examples?
environmental time cues that helps maintain biological clock
eg. light
what is entrainment?
process when a bio clock is reset to match environmental changes through the influence of a zeitgeber
- eg. circadian rhythms are entrained to the day-night cycle
what is the role of the SCN?
- suprachiasmatic nucleus of the hypothalamus -> master biological clock that regulates sleep
- receives info about the amount of incoming light from the eyes and adjusts our sleep-wake cycle accordingly
- sends messages to the pineal gland to secrete more/less melatonin
- low lvl light= higher melatonin lvls= more drowsiness/less alertness
what are ultradian rhythms?
cycle that involves changes in bodily functions or activities that occur shorter than 24 hours
eg. sleep cycle
- one complete sleep cycle≈ 90 minutes
what are the key features of NREM?
- 75-80% of our sleep with more time spent in NREM during the first half of the night
- one sleep cycle: NREM stage 1, 2, 3, 4, 3, 2 REM (approx 90 mins) usually skipping s1
- sleep episode: Typically 4-5 sleep cycles in one night (for an adult)
- progressed through from lightest sleep (s1) through to deepest sleep (s4) then back through lighter stages of sleep
- generally characterized by a reduction in physiological activity
what is sleep onset/hypnogogic state?
transition period between wakefulness and sleep
- emg: begin to relax
- eog: little eye movement
- arousal threshold: low= easy to wake
- may experience unusual hallucinatory perceptual experiences (flashes of light, vivid images) and a sense of falling
what are the key characteristics of NREM stage 1?
occurs as we drift into and out of true sleeo:
- emg: muscles relax, can have muscle twitches/spasms= burst of electrical activity
- eog: slow rolling eye movement
- arousal threshold: low= easily woken
- dreaming: not likely to occur
- changes in duration across sleep: only occur in the first sleep cycle: 4-5% of total sleep time
what are the key features of NREM stage 2?
light stage of sleep but considered “true sleep”
- emg: continue to decrease= less electrical activity
- eog: eye movements stop
- arousal threshold: higher than s1= fairly easy to wake but requires more intense stimuli to wake
- dreaming= possible but not likely
- changes in duration across sleep: each successive cycle lengthens≈ 45-55% of total sleep time
what are the key features of NREM s3?
moderately deep sleep
- emg: extremely relaxed= very little electrical activity
- eog: lack of eye movement= very little electrical activity
- arousal threshold: higher than s2 ➝ less responsive to stimuli= when woken, feels groggy & disorientated
- dreaming: possible
- changes in duration across sleep: occur in 3 sleep cycles= may not enter s3 in latter half➝ 3-8% total sleep time
what are the key features of NREM s4?
deepest stage of sleep
- emg: completely relaxed= very little activity, barely any movement
- eog: no eye movement
- arousal threshold: highest= really difficult to wake➝ takes several minutes to orientate themselves
- dreaming: possible
- changes in duration across sleep: occur in the first 2 cycles ➝ 20-40 minutes but reduces as the night progresses; 10-15% of total sleep time
what is REM sleep?
paradoxical sleep: internally very active but outwardly very calm
- can be considered light sleep: increased brainwave activity
- & deep sleep: decreased muscle tone
what are the characteristics of REM sleep?
- emg: very still with occasional twitching movements= like paralysis (but muscle tone is at its lowest
- eog: spontaneous, rapid, jerky eye movement and bursts of movement
- arousal threshold: high= usually quite difficult to wake (depends on when during the REM period, awakening is attempted) like s2 or s4
- dreaming: most dreaming occurs & tends to follow a storyline
- changes in duration across sleep: lengthens and occur closer in time together as sleep episode progresses➝ 20-25% of total sleep time
what are the brain wave patterns in the sleep stages
NREM: 1 - alpha; 2 - mostly theta; 3- theta+delta (20-50%); 4 - theta+ delta (>50%)
REM: beta-like waves (irregular high frequency, low amplitude with a ‘sawtooth’ pattern)
what does the restoration theory of sleep propose about the purpose and function of sleep?
sleep allows us to recharge our bodies and recover from the mental and physical activities of the day
- allows the body to replenish resources that have been used
eg. neurotransmitters needed for communication between neurons, damaged cells to be repaired, muscles to be detoxified or rid themselves of waste products
what evidence supports the restoration theory?
- people report feeling refreshed and energised after sleep
- people tend to sleep longer when they are sick
- growth hormone (which promotes body repair) is secreted at higher rates during sleep
- muscles are relaxed= period of physiological rest
what are the restorative effects of NREM sleep?
restoration of the body
- physical growth
- tissue repair
- recovery from the effects of fatigue
what are the restorative effects of REM sleep?
restoration of the brain
- contributes to brain growth and development
- provides exercise to neural circuits by increasing brain activity
- assist in consolidating memories and improve learning
what is REM rebound?
catching up on REM sleep by spending more time than usual in it immediately following a period of lost REM sleep
what are some limitations of the restoration theory?
- studies have not conclusively established a cause-effect way of what is being repaired during sleep
- studies show we don’t require more sleep when we exercise➝ people with limited mobility need as much sleep as active people= restoration cannot be the only purpose of sleep
- need for sleep does not disappear following rest
- high activity during REM uses energy= body is not always ‘rested’ during sleep
what is the purpose and function of the evolutionary theory?
sleep serves as a means to increase an animal’s chances of survival in its environment by making them inactive during the part of the day when it’s most dangerous to move about.
- circadian sleep-wake cycle help ensure its lifestyle and specific activities are synchronised with the day-night cycle of its environment
- once survival functions are fulfilled (eating, drinking, reproducing, caring for young)= it needs to conserves energy and protects itself from predators (less likely to attract attention when sleep
what is evidence supports the evolutionary theory?
- sleep-wake cycle regulated by circadian rhythms that are ties to light-dark changes= supports safer lifestyle
eg. hunt for food in the day when you can see - easy to obtain food= more sleep (few natural predators; lions, gorillas)
- easy to hide= more sleep (smaller animals; possums, bats)
- more vulnerable to attack= less sleep (grazing animals exposed out in the open; horses, cows)
what are some limitations to the evolutionary theory?
- doesn’t explain our need for sleep (assumes sleep is useful not essential)
- doesn’t explain the loss of awareness during sleep= more vulnerable to attack when sleeping
(safer to remain in a state of heightened conscious awareness= contradicts) - doesn’t explain why we eventually sleep regardless of environmental circumstances
eg. muscles are in a relaxed state= not ready to respond to danger
what are limitations of both theories?
- supporting evidence is limited
- overlook the benefits of sleep that contribute to our mental wellbeing
- don’t account for the ultradian nature of sleep➝ patterns/proportions of NREM/REM sleep
what are the 2 main changes that occur to sleep patterns across the lifespan?
- the total time spent sleeping tends to get shorter as we get older
- the total time spent in REM decreases dramatically between birth and age 2, then remains relatively stable
what is the expected sleep patterns of a neonate (newborn?)
- no regular rhythm= sleep onset occurs at anytime
- sleep duration is irregular= ranges from 30mins-4 hour
total sleep time: 16 hours
NREM: 50%
REM: 50%
what is the expected sleep patterns of an infant?
sleep cycle becomes more regular
total sleep time: 14-15 hours
NREM: full NREM cycle emerges- 70%
REM: muscle paralysis starts- 30%
what is the expected sleep patterns of young children?
decrease in total time= introduction of school routine & maturation
total sleep time: 11-13 hours
NREM: proportion increases- 75-80%
REM: proportion decreases- 20-25%
what is the expected sleep pattern of adolescents?
total sleep time: decreases- 9-10 hours
NREM: increase in s2- 75-80%
REM: 20-25%
what is the expected sleep pattern of adults/elderly?
- sleep less as they age
- more fragmented sleep/more awakenings
- sleepier in early evening & wake up earlier in the morning
total sleep time: typically 6-8 hours
NREM: gradual loss of NREM stages 3+4- 75-80%
REM: 20-25%
