Sleep: purpose & function Flashcards
A typical night of sleep is…
7-8 hours, in 1.5 hour sleep cycles
NREM periods decrease as the night progresses.
REM periods increase as the night progresses.
What is NREM sleep?
Non-rapid eye movement sleep. As adults, we spend 80% of sleep in NREM
What is REM sleep?
Rapid-eye movement sleep. As adults we spend 20% of sleep in REM.
What is a circadian rhythm?
24 hour cycle. E.g. Sleep-wake cycle
What is an ultradian rhythm?
Cycle that is less than 24 hours E.g. REM and NREM sleep cycles
What is an infradian rhythm
Cycle that is more than 24 hours E.g. Menstrual cycle
What is a circadian rhythm determined by?
Controlled by an internal body clock called the suprachiasmatic nucleus which is located in the hypothalamus, which monitors the release of melatonin from the pineal gland.
What is melatonin?
A sleep hormone that is secreted from the pineal gland which is released when it is dark, and is stopped when it is light
What affects the suprachiasmatic nucleus?
Exposure to light causes the suprachiasmatic nucleus to signal to the pineal gland to stop releasing melatonin.
> Light in the morning can lead to waking (phase shift)
Light in the evening can keep us awake (phase delay).
In a full night’s sleep how do the NREM/REM stages transition?
> NREM 1
NREM 2
NREM 3
NREM 4
> NREM 3
NREM 2
> REM
What happens in NREM 1?
> Transition between awake and being asleep
> Time: Between 30 seconds to 10 minutes
> Theta waves
> Hallucinatory images
Hypnic jerks (involuntary muscle twitches )
Easily awakened
What happens in NREM 2?
> True sleep begins, first part of NREM/REM sleep cycle
> Time: 20 minutes
> More theta waves + k-complex waves (sharp rise and falls in amplitude) and sleep spindles (periodic bursts of rapid frequency)
> 50% of our total sleep
Fairly easily awakened
Eyes stop rolling and muscles more relaxed
What happens in NREM 3?
> Brief transitional stage that makes the start of deep sleep
> Time: 20 minutes
> Delta waves
> Less responsive to external stimuli
If awoken, feel groggy
Eyes don’t move, muscles are relaxed, and heart rate and breathing rate are reduced
What happens in NREM 4?
> Deepest sleep
> Time: 30 minutes in the 1st cycle, decreasing in duration
> Delta waves
> Extremely difficult to wake up someone
Conscious awareness is very low; sensitive to certain stimuli
Sleep walking, sleep talking, bedwetting, night terrors
What happens in REM?
> Paradoxical sleep → active mind, paralysed body
> Time: 10 minutes in 1st cycle, increasing in duration
> Sawtooth waves are random, fast waves, also known as beta-like waves and are associated with dreaming.
> Repetitive bursts of rapid eye moving
Heart rate, blood pressure and breathing rate increase/fluctuate
No muscle tension → muscles are very relaxed that they almost appear paralysed (muscle atonia/cataplexy)
What is the evolutionary theory of sleep?
It states that sleep is a means of increasing an animal’s chances of survival.
> Sleep depends on an animal’s vulnerability to predators. Prey tend to sleep less, especially when exposed in their environment, whereas natural predators often sleep for long periods. Sleep is also
What limitations/criticisms of the evolutionary theory of sleep?
> The evolutionary theory assumes that sleep is useful but not essential, and fails to explain the necessity of sleep, regardless of the level of danger and food sources available.
> The theory assumes that sleeping is a way of hiding from predators, while sleeping makes animals more vulnerable due to their loss of awareness during sleep.
What is the Restoration Theory of Sleep?
Sleep allows us to recharge our bodies, and to grow and recover from the fatigue of physical and psychological work during the day.
What is the biological evidence for the Restoration Theory of Sleep?
The neurotransmitter adenosine (produced when cells use energy) is a cellular waste product that accumulates when we’re awake, making us feel sleepy (as sleep is where we get rid of wastes).
What is a hypnogocic state?
Rolling into the first stage of sleep
What is the hypnopompic state?
Rolling out of sleep.
What limitations/criticisms of for Restoration Theory of Sleep?
> Bedridden people’s sleep patterns are similar to normally active individuals
> Assumes that the body rests during sleep, whilst the brain is active during sleep.
What is the ratio of REM to NREM for babies?
50% REM
50% NREM
What is the ratio of REM to NREM for teenagers + adults?
20% REM
80% NREM
What is the ratio of REM to NREM for elderly?
15% REM
85% NREM
What are zietgebers factor?
External or environmental cues that affect the sleep-wake cycle. E.g. level of light in the room
What are endogenous factors?
Internal factors that influence the sleep-wake cycle. E.g. low levels of melatonin
