Why do we need sleep?
- sleep takes up almost 1/3 of our lives
- when deprived of it, we feel terrible and our performance suffers
- researchers, however, are not sure exactly why we need sleep – just that we do
What are the effects of lack of sleep?
- Major effects
- fatigue
- diminished immunity to disease
- slight hand tremor
- irritability
- inattention
- when performing monotonous activities, results can be devastating (i.e. driving)
- on short, highly motivating tasks there is little effect
- lack of sleep affects everyone differently
The Categories of Sleep
- There are two major categories of sleep: NREM and REM sleep
- REM Sleep (Rapid Eye Movement)
- makes up 20 – 25% of a normal nights sleep
- a sleeper will experience:
- rapid eye movements
- a rush of Epinephrine (adrenaline)
- blood pressure rises
- heart rate and respiration become faster and irregular
- brain temperature increases
- large muscles of the body become paralyzed
- vivid dreams
- NREM Sleep (Non-Rapid Eye Movement)
- makes up 75 – 80% of a normal nights sleep
- there are four stages of NREM sleep
- a sleeper will experience:
- no rapid eye movements
- heart rate and respiration that is slow and regular
- little body movement
- blood pressure and brain activity are at their lowest points of the 24-hour period
The Stages of NREM Sleep
- sleep follows a fairly predictable pattern every night – we sleep in cycles
- each cycle lasts approximately 90 minutes, and consists of one or more stages of NREM sleep, which is then followed by a period of REM sleep
- The stages of NREM sleep:
- Stage One:
- a few minutes long
- very light sleep
- the transition between waking and sleeping
- Stage Two:
- 50% of a night’s sleep
- a somewhat deeper sleep
- sleeper is harder to awaken
- Stage Three:
- a few minutes long
- the beginning of slow-wave sleep (aka. deep sleep)
- sleep gradually becomes deeper and deeper
- growth hormone is secreted
- Stage Four:
- approximately 40 minutes long
- slow-wave sleep – the deepest sleep
- sleeper is the hardest to awaken
- growth hormone is secreted
- Stage One:
The Complete Sleep Cycle (1, 2, 3, 4, 3, 2, REM)
- NREM sleep descends from stage 1 to stage 4
- goes back to stages 3 and 2
- Enters the first REM period of the night (REM lasts 10 – 15 minutes)
- at the end of this REM cycle, the first sleep cycle is complete
- sleep goes from the REM period to stage 2 sleep, and follows the same cycle as before
- after 2 cycles (approx. 3 hours), sleepers will usually get no more stage 4 sleep and the REM period gets longer
- most people sleep about 5 sleep cycles (7.5 – 8 hours) per night
- results in 1.5 hours of slow-wave sleep and 1.5 hours of REM sleep
