Lesson 3: Characteristics and Patterns of Sleep

http://www.youtube.com/watch?v=t27suXgfi8w

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Characteristics of Sleep

NREM Sleep Non-rapid eye movement sleep

NREM sleep includes those stages not associated with rapid eye movements. Adults spend approximately 80 percent of their nights sleep in NREM, and typically the first half of the night has more NREM sleep than the second half.

NREM is essential to the physical growth and repair of the body. Research has found the amount of NREM increases after vigorous exercise (Vein et al., 1991).

NREM is dream free about 90% of the time, dreams tend to be more short lived and fragmented than those in REM.

NREM Stage 1

~Theta waves, which are of lower frequency and higher amplitude than alpha waves, appear and start to replace alpha waves.

~Despite the fact that various wave types are shown in this stage, theta waves define Stage 1 NREM sleep.

~In stage one of sleep, breathing becomes irregular, muscles relax, and hypnogogic jerks often occur.

~Stage 1 lasts for approximately 5 min but this can vary.

NREM Stage 2

~In this stage there is a prevalence of theta-wave activity.

~ As sleep deepens EEG recordings begin to pick up unique brain wave features that are characteristic of stage 2 sleep. Theses include

• Sleep spindles – brief bursts of higher frequency brain waves • K complexes – single sharp bursts (rise then fall) in amplitude (and

lower frequency). • Body temperature decreases • Breathing and heart rate decrease • ~Stage 2 sleep lasts for approximately 20 min

NREM Stage 3

~Delta waves begin to appear which are large and slow.

~Stage 3 is a transitional stage and lasts for approximately 10 min.

NREM Stage 4

~Brain waves become almost pure delta waves

~Regular (slow) heartbeat, slow (rhythmic) respiration & little muscle activity

~ Lasts for approximately 30 min

~Very hard to awaken a sleeper from Stage 4 sleep.

REM ~ Rapid Eye Movement~REM sleep is strongly associated with dreaming. About 85% of the time a person is awakened from REM sleep they report vivid dreams.

~ The brain wave pattern associated with REM sleep is irregular, consisting of low-

amplitude, relatively high-frequency beta waves, like those produced during alert wakefulness.

~On average REM sleep totals about 90 min per night. The amount of REM sleep tends increases with stress in an individuals life.~REM sleep is sometimes called paradoxical sleep, as aspects of REM sleep appear to

contradict each other. The brain wave pattern is very much like those produced during alert wakefulness. The bodies internal functioning is more active during REM sleep than during NREM sleep, the heart beats faster, breathing is more rapid and irregular, and genitals become aroused. On the other hand, the sleeper is totally relaxed; most of the skeletal muscles are totally relaxed (to the point of paralysis).

Patterns of SleepAn adult sleeps for approximately 8 hrs per night progressing through cycles of about 1.5 hours. Periods of deep sleep (NREM4) occur earlier in the night, and periods of REM sleep occur, on average every 90 minutes.

Adults experience a total of 1-2 hours REM sleep a night, in 4-5 sessions, each progressing in length.

The period of total REM sleep lessons as individuals get older. A newborn spends approximately 50% of total time in REM sleep compared to an adult who spends approximately 20% of their time in REM sleep.

WHY DO WE SLEEP?

Survival Theories

Focuses on when and why different species sleep

Sleep depends on the need to find food

Sleep depends on an animal’s vulnerability to predators

Sleep conserves energy

Limitations of Survival Theories

Survival theories state that sleeping offers security from predators, however the loss of awareness while asleep

contradicts this statement.

Survival theories fail to explain why we MUST sleep

Restorative Theories

Focuses on why sleep is important

Sleep enhances mood

Sleep repairs and replenishes the body and prepares it for action the next day

The neurotransmitters adenosine (energy), norepinephrine (alertness)

Metabolism

Growth hormones

Immunity to disease

Consolidates memories

Limitations of Restorative Theories

The body does not completely “rest” during sleep (REM) as assumed by restorative theories

Lack of physical activity does not reduce the amount of sleep needed