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Sleep is an integral part of being a human and is what enables us to function successfully during the day. Having adequate sleep is vital in ensuring our overall health both physically and mentally. This is shown by the fact that when we don’t get a good night’s sleep, we usually do not feel completely ‘right’ the following day and, if this persists, we can find ourselves feeling worse and worse as the days pass.
Although it is not fully understood why we sleep, researchers believe that it is key in healing, memory function and learning. When we sleep we ‘regenerate’ ourselves so that we are energised and ready to start a new day and when we fail to sleep properly, this is what leads to feelings of lethargy.
The four sleep stages
There are four stages of sleep (five if REM sleep is included) and each stage will appear more than once throughout a period of sleep. ECGs show the different brain activity that is going on when a person is asleep and this can help to identify which stage of sleep is occurring. The table below outlines each of the four stages of sleep:
| Stage | What occurs during the stage |
|---|---|
| 1 – sleep onset | Light sleep Easily woken Muscles become less active Eye movements slow Sudden twitches are normal Alpha and theta brainwaves are occurring; alpha brain activity is considered restful. |
| 2 – the ‘late night stage’ | Brainwaves are slower (theta brainwaves) Eye movements stop completely Body temperature drops Heart rate slows Stage between sleep onset and sleep. |
| 3 – deep sleep | Slow delta brainwaves but some faster ones too Stage between light and deep sleep. |
| 4 – deep sleep | Almost all brainwaves are slow, delta Very hard to wake someone No eye movements Feel disoriented if woken in this stage Stage most likely to be in when sleep walking occurs. |
REMÂ
All four stages in the table above are known as NREM sleep, however, a fifth sleep stage, known as REM sleep, occurs when a person has rapid eye movements (hence REM) and a person’s eyelids will move very quickly. Dreaming tends to also occur during this phase and the phase is thought to last for about two hours of an average night’s sleep.
When someone is going through a stage of REM sleep, their senses are blocked; this is referred to as sensory blockade. During this phase, muscles are paralysed and breathing will become rapid, shallow and irregular. Heart rate and blood pressure can both increase.
The sleep cycle
- A person goes through about five cycles of sleep stages
- One cycle of sleep lasts about 90 minutes
- Cycle one has a short REM period and more deep sleep
- As cycles progress, REM sleep lasts longer and deep sleep reduces
- By morning a person will be in stages 1 and 2 and in REM sleep
What functions and benefits does sleep have?
An average adult needs approximately 7 or 8 hours of sleep per night, although this will fluctuate, dependent upon individual need. If sleep is missed, it can be caught up on but people tend to find that as they get older, they need less sleep; this may be due to the natural ageing process but may also be because of things like medication or physical ailments.
When a person does not get enough sleep, this is referred to as being sleep deprived. Consequences of being sleep deprived cause a reduction in cognitive functioning, which means that things like memory, thinking and perception will be affected.
Sleep is thought to be linked to learning, as much of what a person has experienced in a day is consolidated into their long-term memory whilst they sleep and it is also thought to be linked to recovery from illness and injury, enabling the body to repair itself and heal.
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