Q3L10 - Sleep

Sleep

Did you know…• Most people spend one-third of

their entire lives asleep?• A new baby typically results in

400-750 hours lost sleep for parents in the first year

• It's impossible to tell if someone is really awake without close medical supervision. People can take cat naps with their eyes open without even being aware of it.

• The record for the longest period without sleep is 18 days, 21 hours, 40 minutes during a rocking chair marathon. The record holder reported hallucinations, paranoia, blurred vision, slurred speech and memory and concentration lapses.

Circadian Rhythms

• The sleep-wake cycle• Latin origins – circa = about;

diem = day• Therefore, a circadian rhythm

is a cycle that takes about a day to complete

• Most people will experience several hours of sleep at least once during a 24 hour period.

• Sleep-wake cycle controlled by an area within the hypothalamus – the suprachiasmatic nucleus (SCN)

SCN• As daylight fades, the SCN tells the pineal gland

(at the base of the brain) to secrete the hormone melatonin.

• As melatonin accumulates, the person will feel sleepy.

• As the light coming to the eyes increases, the SCN tells the pineal gland to stop secreting melatonin, allowing the body to awaken

• In studies where volunteers spend several days without access to information about day or night, their sleep-wake cycle lengthened to 25 hours (Czeisler, 1995; Czeisler, 1980)

• Based on this research, it appears the SCN may be responsible for resetting the body’s biological clock to a 24 hour cycle every day.

• British Ministry of Defence researchers have been able to reset soldiers' body clocks so they can go without sleep for up to 36 hrs. Tiny optical fibres embedded in special spectacles project a ring of bright white light (with a spectrum identical to a sunrise) around the edge of soldiers' retinas, fooling them into thinking they have just woken up. The system was first used on US pilots during the bombing of Kosovo.

Stages of Sleep

• Non-REM – much deeper, more restful sleep

- Stage 1- Stage 2- Stage 3- Stage 4• REM – where dreaming

takes place

• EEG is used to see brain wave activity in the various stages

NON-REM: Stage One

• Theta activity (slower and larger than alpha waves)

• Border between waking and sleep• If awaken, people may not believe they were

asleep• May experience vivid visual events (hypnagogic

images) which may become dreams but often seen as flashes of light

• Hypnic jerks muscles are so tensed up from the day that the brain instructs the body to ‘shake it out’

NON-REM: Stage Two

• EEG will show first sign of sleep spindles (brief bursts of activity lasting only a second or two)

• Theta waves still predominate, but if awaken people will be aware of having been asleep

• Body temperature continues to drop, heart rate slows, breathing becomes more shallow and irregular

NON-REM: Stage Three

• Delta wave activity (the slowest and largest waves)

• In Stage 3, Delta waves make up only 20-50% of brain wave pattern

NON-REM: Stage Four

• Delta waves account for 50% + of the total brain activity and will eventually make up 100%

• Deepest stage of sleep• Growth hormones are released from pituitary glands and

reach their peak• Body is at the lowest level of functioning• Very hard to awaken – may be confused/disorientated• Children need deep sleep for their bodies to grow and

are harder to wake up than adults• May explain why sleep disorders being more common in

childhood and in boys (high levels of testosterone)

REM sleep

• Rapid Eye Movement• Body is almost as aroused as in a waking state, but is

also paralysed• Brain waves resemble beta waves• When awakened, the person almost always reports being

in a dream state• 90% of dreams actually take place in REM sleep.• Dreams can be in Non-REM stages, but REM dreams

tend to be more vivid, more detailed, longer and more bizarre.

• Non-REM dreams tend to be more like thoughts about daily occurrences and far shorter.

• If deprived of REM sleep, a person will experience greatly increased amounts the next night – REM rebound

Why two kinds of sleep?

• After a physically demanding day, people tend to spend more time in Non-REM deep sleep than usual

• An emotionally stressful day leads to increased time in REM sleep.

Non-REM and REM Sleep Disorders

• Sleepwalking• Night Terrors• Nightmares• REM Behaviour

Disorder

Sleepwalking• Somnambulism• 20% of population• Partly due to heredity• More common in childhood and in

boys• Range from sitting up in bed to

walking around the house, looking in the fridge and getting into the car.

• Lack of memory is typical in most cases

• Clear obstacles; prevent sleep loss

• Not dangerous to wake sleepwalkers!

• In Stage Four – NOT REM… therefore, NOT dreamers acting out a dream

Night Terrors

• State of panic while sound asleep

• People may sit up, run around the room, scream or find it difficult to breathe.

• Most do not remember what happened during an episode

• Happens in Non-REM sleep

Nightmares

• Vividly remembered immediately upon waking

• Happens during REM sleep, thus people don’t move around in a nightmare as they do in a night terror

• Children tend to have more as they spend more of their sleep in REM

REM Behaviour Disorder

• Acting out one’s dreams.• Rare disorder in which

the brain mechanisms that normally inhibit the voluntary muscles fail, allowing the person to thrash around

• Usually seen in men over age 60, possible connection with neurodegenerative diseases, dementia and Parkinson’s disease.