This is a topic we cover in one of our Driver CPC training days.  Want to know more from an expert instructor? Have a look at the 'Tiredness, Diet and Lifestyle' course for more.

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Feeling tired? Read on - it's important!

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Sleep is vital to us for lots of reasons, yet it's one of those things we often take for granted.  So what's going on?

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Its all about cycles!

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Many people believe that our brains rest while we sleep, however scientific research has revealed the processes that occur in sleep.

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Sleep restores our bodies, strengthens our immune systems and enables healthy, balanced mental and emotional functioning.

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An average adult sleeps 7 - 9 hours a night; those involved with haulage often lower, around 6 - 7 hours of sleep.

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The night sleep is split into individual sleep zones, which change as the night progresses. It is important to know how sleep works to allow you to manage sleep, particularly if you have to wake at particular times or when sleeping in unfamiliar places.

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Stages of Sleep

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The sleep-wake cycle is controlled by the brain (actually the suprachiasmatic nucleus (SCN) located in the hypothalamus).  Receptors in the eye (melanopsin receptors in the retina) respond to light levels and send signals to the brain through the optic nerve. The pineal gland in the brain produces melatonin in response to low light (especially blue) levels.  Production of melatonin starts typically around 9pm and continues for around 12 hours which causes sleepiness and encourages a person to maintain a sleepy state. During the day, melatonin levels fall to very low levels.

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Awake - Alert

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Brain fully conscious and responsive, producing high frequency beta waves.

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Awake - Tired

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Brain produces alpha waves, and the person wants or needs sleep.

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Stage N1 - Very light sleep

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The nodding off stage takes up about 5-10% of the total sleep time, and is non-REM sleep.  The brain changes to different modes, producing theta waves as this happens.  As we drift off, we occasionally twitch - these are known as hypnogogic or myoclonic jerks - particular as a result of falling dreams.

Obstructive sleep apnoea (OSA) increases this type of sleep at the expense of deeper, more restorative sleep.  This causes sufferers to feel tired when waking up after sleep.

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Stage N2 - Light sleep

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This stage takes up 50% of the total night sleep. In this stage. heart rate slows, core temperature drops and the body prepares to go into deep sleep. The brain produces K-complexes and sleep spindles as can be seen on EEGs (these are 'brain wave charts', electroencephalograms).

This is the stage where bruxism (grinding of teeth) occurs most often.

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Stage N3 - Deep sleep (restorative, delta, slow wave sleep)

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This stage is also called slow wave sleep or delta sleep and is the deepest sleep. 

 

This type makes up 10-20% of the total night sleep.  Interestingly, the length of this type of sleep goes down through the night, with most restorative sleep occurring earlier on.  This stage reduces our requirement for sleep. 

 

Lots of physical processes occur here - human growth hormone is released and the immune system refreshes.  Deep sleeping in day (i.e. 90 minutes or more) reduces restorative sleep at night and could cause an increase in the time it takes to get to sleep. The brain produces delta waves, which appear as slow waves on an EEG. 

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If someone in this stage is woken abruptly, they have sleep inertia which causes disorientation and various cognitive issues as the person struggles to perform as they would normally do.

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This is the stage where people suffer from night terrors, sleep walking and sleep talking. A lot of dreaming occurs here, but there is usually no recollection due to deep sleep.

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REM sleep

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Rapid eye movement sleep, also known as paradoxical sleep.  The brain produces beta waves, just like it does when awake and alert. Various autonomic changes occur such as an increase in heart rate and blood pressure. About 15% of the total sleep is in this stage. 

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During REM sleep, a person often has vivid and powerful dreams which are often accompanied by muscle paralysis.  REM sleep increases with each cycle through the night, with the last REM cycle lasting perhaps an hour alone.

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Major depressive disorder causes a person to go into REM sleep faster and an increase of REM duration, especially for the first cycle.  Overall the person goes into REM more often, with greater duration.

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Putting it all together

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A sleep cycle will go from light to deep sleep, then back up to REM.  The first sleep cycle lasts approximately 90 minutes, then become longer up to 100-120 minutes.  A full night sleep averages around 4 - 5 sleep cycles.

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