What is a Circadian Rhythm?
Biological Rhythms that occur approximately once every 24 hours.
The Sleep/Wake cycle is an example of a Circadian Rhythm.
What are the characteristics of sleep as an altered state of consciousness?
- Level of awareness - not awake, nor unconscious
- Fewer content limitations
- Controlled and automatic processes are impossible
- Perceptual and Cognitive Distortions
- More or less emotional awareness
- Less self control
- Distorted time orientation
What is an Infradian Rhythm?
Biological rhythms with cycles longer than 24 hours.
(i.e. migration patterns)
What is an Ultradian Rhythm?
Biological rhythms with cycles shorter than 24 hours.
(i.e. NREM/REM sleep)
How long is a normal sleep cycle?
How many cycles to typical adults experience each night?
4-6 NREM/REM cycles per night
Stage 1 NREM sleep
Stage 1 NREM sleep is brief, lasting around 5 minutes for most people (ranges from 30 seconds to 10 minutes). It is a very light sleep from which we can be easily awakened. It is sometimes called the presleep stage.
Alpha waves begin to be replaced by slower lower frequency and higher amplitude theta waves.
Stage 2 NREM Sleep
Considered the point at which true sleep begins. Characterised by Sleep Spindles and K-Complexes among the theta waves.
Stage 2 Sleep accounts for about 50% of our total sleep.
Stage 3 NREM sleep
Brief transitional stage that marks the start of deep sleep (slow wave sleep). During stage 3, we become less responsive to external stimuli and more difficult to awaken.
If awoken feel groggy and disorientated.
Delta waves become more common (20% to 50% of the time)
Stage 4 NREM sleep
Deepest sleep. Extremely difficult to be awoken.
Brainwaves consists of regular, slow and large delta waves for more than 50% of the time.
What is slow wave sleep?
Slow wave sleep is the collective name for stages 3 and 4 of NREM sleep.
What is somnambulism?
Somnambulism is sleepwalking and is more common in children (7%) compared to adults (2%). It occurs during stage 3 & 4 of NREM sleep.
What are night terrors?
Night terrors occur in stages 3 & 4 NREM sleep, a time when voluntary muscles are very relaxed but still able to move.
Night terrors are extremely frightening episodes where the person wakes and often screams in sheer terror. Although the person is often sweating, with rapid heart and breathing rates, he or she has little or no recall of dreaming and often falls asleep again very quickly.
What are nightmares?
Occur in REM sleep and are more likely to be remembered than night terrors. More common in children than adults although women experience them twice as much as men in adulthood. Little physiological changes and little movement.
Nightmares are usually remembered.
Rapid Eye Movement (REM) Sleep
As the name suggests your eyes move rapidly for short bursts of time. The first cycle lasts about 10 minutes. Everyone dreams during REM sleep and will report they were dreaming if awoken during this period. Most dreaming occurs during REM sleep, however about 10% of our dreams occur during NREM sleep.
Your heart rate, blood pressure and respiration increase and fluctuate. Body temperature generally matches the surrounding environment.
All muscles are very relaxed to the point of being almost paralysed. This paralysis is known as muscle atonia or cataplexy.
What is a hypnogram?
Sleep cycles are recorded and plotted onto a graph known as a hypnogram.
Define hypnopompic state
The period between being asleep and waking up, a time when brainwaves are predominately alpha waves.
We may experience vivid visual images during this time, known as hypnopompic images.
How do sleep patterns change as we age?
Newborns spend about 16 hours per day sleeping, with about half of this time in REM sleep.
Adults sleep for about 8 hours, with about a quarter of this in REM sleep.
By the age of 60 years, very little time, if any, is spent in stage 4 NREM sleep with sleep lasting for about 6 hours - still with 20-25% in REM sleep.
What is the Survival (adaptive and evolutionary theories of sleep)?
According to this theory, survival is the main purpose of sleep. Sleep is a means of increasing an animal's chances of survival in its environment.
- Sleep depends on the need to find food (animals that need to graze for hours sleep less - i.e. cows)
- Sleep depends on an animal's vulnerability to predators (small animals which are more vulnerable sleep more - i.e. mice)
- Sleep conserves energy (when an animal sleeps, its metabolism slows, thus reducing the need for food)
Criticisms of the Survival (adaptive and evolutionary) theories of sleep
- Does not explain why we must sleep (only that it is useful)
- The assumption that sleeping is a way to safely hide from predators but for animals that are highly preyed upon sleeping is very dangerous.
What is the Restorative (restore and recover) theories of sleep
Sleep allows us to recharge our bodies, recover from physical and psychological work during the day and allows our bodies' growth processes to function.
- Sleep repairs and replenishes the body and prepares it for action the next day
- Sleep enhances mood
- Sleep activates growth hormones
- Sleep increases immunity to disease
- Sleep increases alertness
- Sleep consolidates memory
Criticisms of the Restorative (restore and recover) theories of sleep