Sleep is something we LOVE to talk about it! In fact, it’s often the first thing we’ll say to our partner in the morning “how did you sleep?”. But actually, how many of us actually know, HOW we sleep?! Here’s your brief introduction to understanding sleep a little bit better. Next time you and your friends chat about your sleep (or lack of), you can showcase your knowledge!
In order to sleep we depend on our circadian rhythm (body clock) to release the hormone melatonin at the correct time in order to feel sleepy or awake at the correct time. External cues influence the regulation of your body clock and can help it to regulate, such as light exposure during the day, eating meals at consistent times and waking at the same time each morning. In partnership with the timely release of melatonin, your body also depends on your sleep drive (homeostasis) to enable sleep. Your sleep drive is essentially a sleep pressure- it builds and builds during a period of wakefulness. When you sleep, this pressure dissipates again. This helps you understand why when you wake in the early hours of the morning it can be really hard to get back to sleep- it’s because most of your sleep pressure has gone since you’ve had several hours of sleep. When you wake after an hour or so of sleep, you still have plenty of sleep pressure to assist you back into the land of nod.
Once asleep, we sleep in cycles. As we end one cycle and before going into another, we will sometimes move back into consciousness (and take a sip of water, go to the toilet, check the time etc) and then fall back to sleep into the next cycle. Adults ideally need five or six full sleep cycles a night to feel rested the following day. An average adult’s sleep cycle is circa 90 minutes. This equates to a sleep requirement of between 7-8 hours sleep each night. Babies sleep cycles are shorter and last around 50 minutes for the first 9 months. As children grow, their sleep cycles lengthen and by school age they are likely to to have similar durations as adults.
A brief summary of the stages of sleep we need are as follows:
Stage 1 - Very light- going from wakefulness to sleep. You are easy to wake in this stage
Stage 2 - Light, dreamless sleep. 50% of adults and children’s night spent in this stage
Stage 3 - Slow-wave deep sleep. Very deep- hard to wake someone in this stage. Refreshing sleep. 25% of night spent in this stage (not elderly) Most of this stage of sleep occurs in first half of the night- hence babies tend to wake parents more after about 4 hours of sleep or more
Stage 4/REM sleep - vivid dreaming occurs, light sleep/easily woken. Typically when nightmares occur, muscles neck down are paralysed for adults and children. Develops over time with babies, hence why young babies are more fidgety and noisy in their sleep. Accounts for 20% of nights sleep. REM sleep is more dominant second half of night
Please note that until babies are around four months, they have shorter sleep cycles and have different sleep stages. They also do their ‘lighter’, REM type sleep first and deeper sleep second- the opposite of adults sleep stages. This is why young babies appear to be deeply asleep in your arms, but then as soon as you try to lay them down, they wake! In order to ensure transferring them without waking, ideally you’d wait until they had transitioned from their light stage of sleep to deeper stage of sleep!
Hopefully from this introduction to sleep, it reassures you of a couple of things! First, that it is normal to wake a few times a night. We all wake between sleep cycles. Where there can be a difficulty is in getting back into another sleep cycle. For example, adults might find they wake at the end of a cycle in the early hours of the morning and their brain ‘kicks’ into gear and then struggle to fall back to sleep. With there being less sleep pressure (having already slept for a few hours) and with the last part of the night’s sleep being more dominated by lighter REM sleep, adults really can struggle to get back to sleep! Children might be dependent on something to fall asleep at the start of the night and so if they wake fully from a sleep cycle, they want the same help to fall back asleep into another cycle, and so signal for a parent to come and assist! Likewise for children, the longer they’ve already been asleep for, the less sleep pressure and so again, this can be a harder time to help them back into another sleep cycle.
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