Sleep is a behavioural state characterised by little physical activity and almost no awareness of the outside world. Most scientists think that sleep does something important — something vital for life, although research has not yet identified specifically what sleep does. Nevertheless, we all know when we need to sleep — we can feel this need. We also know when sleep has done its work — we feel rested and that we have slept enough. Although a sleeper may appear to be unconscious; unlike someone who is actually knocked-out, anesthetized or in a coma; a sleeping person can be easily awakened and can resume normal waking activity within a minute or two.
Sleep is an active, highly organized sequence of events and physiological conditions. Sleep is actually made up of two separate and distinctly different states: ‘non-rapid eye movement sleep (NREM sleep) and ‘rapid eye movement sleep’ (REM sleep) or dreaming sleep. The NREM and REM types of sleep are as different from one another as both are different from wakefulness.
NREM sleep is further divided into stages 1 – 3 (N1 – N3) based on the size and speed of the brain waves generated by the sleeper. Stage 3 of NREM sleep have the biggest and slowest brain waves. These big, slow waves are called delta waves and stage N3 sleep is often called ‘slow-wave sleep’ or ‘delta sleep’. People in stage N3 sleep require the most stimulation to awaken. Therefore, this phase of sleep is often thought of as ‘deep sleep’. Also, large spurts of growth hormone are secreted during stages 3 and 4 NREM sleep. Consequently, Deep Stage N3 Sleep, is thought to restore the body from the wear and tear of waking activity.
During REM sleep (Stage R) you can watch the sleeper’s eyes move around beneath closed eyelids and may indicate a dreaming state. We are almost completely paralyzed in REM sleep and have almost no muscle tone— only the heart, diaphragm, eye muscles and the smooth muscles (such as the muscles of the intestines and blood vessels) are spared from the paralysis of REM sleep. Stage R Sleep can be thought of as “ A Highly Activated Brain in a Paralysed Body”.
There are many theories about the function of REM sleep and dreaming — ranging from ‘safe, socially acceptable, wish fulfilment’ to ‘consolidation of memories’ to ‘providing necessary stimulation to the entire nervous system during development’. Whatever REM sleep does, it is clear that every aspect of existence, from the body’s manufacture of proteins to sexual arousal including orgasm, is influenced by REM sleep. It is likely that the ultimate explanation of REM sleep will be very broad — not simply focused on one physiologic function.
How much sleep you need changes as you age.
- Hirshkowitz M, Whiton K, Albert SM, Alessi C, Bruni O, et al. The National Sleep Foundation’s sleep time duration recommendations: methodology and results summary. Sleep Health. 2015;1(1):40–43
It is important to recognise that when assessing your sleep as being adequate you should assess two elements – the Two Q’s of Sleep:
- Sleep Quantity – The amount of Sleep you are getting
- Sleep Quality – How refreshing and fulfilling your sleep actually is – when Sleep Quality is impacted one feels unrested, unrefreshed despite getting adequate Quantity of sleep. Sleep Disorders (other than insomnia) impact Sleep Quality