• Sleep is a physical and mental resting state
in which a person becomes relatively inactive and unaware
of the environment.
• Normal sleep is characterized by a decrease in body
temperature, blood pressure, breathing rate and most other
body functions
but the brain remains active.
• Wakefulness is a state of awareness in which the
individual is conscious of his/her surrounding environment
and is able
to react with it.
Sleep Cycle
Sleep is characterized by two distinct states, non-REM sleep
and REM sleep that alternate in 90 to 110-minute cycles.
A normal sleep pattern has 4-5 cycles throughout the night.
Non-REM sleep consists of four stages that range from light
dozing to deep sleep. Approximately 75% of night’s
sleep is spent in non-REM sleep.
Stage 1 Sleep
is a transition period from wakefulness to sleep. It is characterized
by slow rolling eye movements, otherwise known as the “dozing” stage.
Approximately 5% of the the total night's sleep should be
spent in Stage 1.
Stage 2 Sleep
is characterized by a lack of eye movements. Brain
waves become larger.
Defined on PSG with sleep spindles and K-complexes. Approximately
45% of the total night's sleep time is spent in Stage 2 of
non-REM sleep. This stage is often considered the official
onset of consolidated sleep. Eye movements stop and brain
waves become larger. Stage 2 Sleep is graphically defined
with two distinct brain wave forms called sleep spindles
and K-complexes. A sleep spindle is a pattern of EEG waves,
consisting of a burst of 11 to 15 hertz waves that last for
.5 to 1.5 seconds. A K-complex is high voltage EEG activity
that consists of a sharp downward component followed by a
slower upward component and lasts more than .5 second.
Stage 3 and Stage
4 or Delta Sleep
Stage 2 sleep evolves into “Delta” sleep
or “slow wave” sleep in approximately 10-20 minutes
and may last 15-30 minutes. It is called “slow wave” sleep
because brain activity slows down dramatically from the “theta” rhythm
of stage 2 to a much slower rhythm of 1 to 2 cycles per second
called “delta” and the height or amplitude of
the waves increases dramatically. In most adults these two
stages are completed within the first two 90 minute sleep
cycles or within the first three hours of sleep. Contrary
to popular belief, it is delta sleep that a sleep deprived
person’s brain craves the first and foremost. In children
unwakeable or “dead asleep” during most of the
night.
Stage 5 Sleep
REM (Rapid Eye Movement Sleep) is a very active stage of
sleep. Most dreaming takes place during REM sleep which is
why you lose muscle tone in REM (so you don’t act out
your dreams). REM sleep composes about 20 – 25% of
the sleep cycle in normal adults. REM sleep is characterized
by:
• |
Eyelid Fluttering |
• |
Rapid Eye Movement |
• |
Muscle Paralysis |
• |
Irregular Breathing |
• |
Decrease in Body Temperature |
• |
Changes in Heart Rate & Blood Pressure |
