Sleep is a complex , very ordered series of events-yet it’s designed to happen naturally without us thinking about it, pretty much the same way that we breathe. If course, if you have a sleep problem, you become very aware of sleep and wakefulness, and it doesn’t seem so easy.
Whether you are a good sleeper or a poor one, it may be useful to find out a little bit about this mysterious thing called sleep. If you are feeling depressed , you will be particularly interested because sleep and depression are closely associated , as we shall see.
So what is sleep?
It is a state of greatly reduced awareness, taking up around one quarter to one third of our daily lives, during which the body repairs itself, and our memories, and emotions are consolidated . There is a lot of evidence that we need sleep for good mental functioning. It is, if you like, nutition for the brain – and we simply can’t do without it . When we are depressed our sleep is often upset , and this is a two-way street, because having insomnia also makes us more likely to get depressed in the first place.
When we measure sleep we look at three different aspects. We measure the brain’s electrical activity with an electroencephalogram (EEG), our musle activity with an electromyogram (EMG) and our eye movements with an electro – oculogram (EOG).
Together , these measurements are called polysomnography (PSG) ; a short-hand way of describing a full sleep assessment.
Stages of sleep
As we fall asleep we go into a transitional phase between wakefulness and sleep known as stage 1. Compared with quiet wakefulness , the EEG slows down , and your muscles begin to relax . If someone wakes yuo up during this very light first stage you might well say,’ Hey, I was just nodding off there!’ or you might startle.
After only a matter of minutes you progress on to stage 2 sleep. Here the EEG varies a lot with what we call ‘mixed frequencies ‘(some fast , some slow, some high amplitude , some low) . However, there are recognizable parts , called ‘K-complexes ‘ and ‘sleep spindles’. Different parts of this stage are important for our attention and memory . Stage 2 actually makes up about 60 per cent of our sleep , although when we first go into it we move quickly through it to the next stages.
Stage 3 and stage 4 arer deep sleep, or slow-wave sleep.We have our deepest sleep during the first couple of hours. I gues most of us would like the idea of having lots of deep sleep, but in fact it makes up only around 10-15 per cent, and less as we get older.Stages 3 and 4 sleep seem important for basic physical recovery growth and tissue repair.
We can see them that sleep involves not only a loss of consciousness , but also a steady change in the EEG. However, there is a form of sleep during which the eyeballs move rapidly (measured by EOG) , whereas the rest of the body is pretty much paralysed (measured by EMG) . The term ‘rapid eye movement ‘ (REM) sleep was coined to describe this.
We could easily injure ourselves by acting out our dreams, were it not for the factthat during REM sleep our muscles are ver relaxed . You may not have realised before that you are in fact ver still in your bed during your dreams, in spite of whatever vivid dream imagery you may experienced. Occasional muscles twitches are quite usual , but any movement on a large scale during REM sleep is uncommon . Although some people think that sleepwalking happens when we dream, in fact it is nothing to do with REM sleep. Sleepwalking and night terrorts happen in our deep sleep.
I will complete in article 4 soon.
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