What Happens When We Sleep?

While sleeping is, of course, essential to the well-being of all animals, humans included, many people don’t realise just how much goes on when they are asleep. Indeed, the average sleep period will be separated into various stages, each of which will include a certain amount of activity in the body.

The Stages

Scientists have concluded that there are essentially five different stages within the sleep cycle, each of which can be identified through the alterations in brain wave activity. However, these stages do not always follow a regular pattern; some stages can be experienced for different lengths of time by different individuals and each stage can be repeated several times during a single sleep period. However, each stage will tend to have certain general characteristics.

Stage 1

This is the stage where the comfort of your small double mattress does its job and the body first begins to fall into sleep. This stage tends to last a short period of time – about 5 per cent of the total sleep cycle, in fact. During this stage, the brain waves will be fairly similar to those that the body experiences during wakefulness.

Stage 2

At this stage the body falls into a far deeper sleep as the breathing and heartbeat slow. This is generally the stage that is the longest of all the sleep stages and on average it will make up about half of the total sleep cycle.

Stages 3 and 4

The body will then fall into an even deeper sleep during these stages as the body relaxes and both breathing and the heartbeat slow considerably. These stages tend to take up between 15 and 25 per cent of the total cycle and are likely to involve dreaming. They might even include sleepwalking.

Stage 5

All the above stages are what are known as non-rapid eye movement (NREM), or quiet sleep, stages. The last stage is the REM stage. This stage actually tends to recur throughout the sleep period and can last for a variety of lengths, from ten minutes to around one hour. During the REM period the body experiences several alterations.

First, the eyes will begin twitching and darting. Second, while brain activity is high during this period and the heartbeat and breathing become significantly faster, the body will, in fact, be at its most relaxed than at any other stage of sleep. Indeed, the body relaxes almost to the point of paralysis. This is largely down to the part of the brain stem named the ‘pons’, which sends signals to the spinal cord telling it to switch off the motor neurons. This both allows people to experience vivid dreams and ensures that they don’t react to them in a dangerous way.

In addition, it is during the REM stage when human memories and emotions are said to be consolidated. This is because the blood flows mostly to the areas of the brain where these aspects are dealt with and less to the areas which are responsible for reasoning and other more complex thought processes. The REM stage, therefore, is important for maintaining a healthy balance.

This guest post has been contributed by Zoe on behalf of Archers Sleep Centre.

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