Sleep is essential for memory consolidation, hormonal regulation, and cellular repair — but what actually happens in the brain during those nightly hours of rest? In this post, Millie explores the science of sleep, looking at circadian rhythms, sleep stages, and brain activity patterns. Read on to find out more.
The science of sleep
Did you know that people spend around one third of their life sleeping? And that the quality and length of sleep greatly affect day-to-day life. But what exactly is the science behind it and why is it so important for our growth and bodies?
What is the circadian rhythm?
Our bodies operate on a 24-hour biological clock called a circadian rhythm, made from a specific sequence of genes switched on and off in the form of proteins. It affects all organisms and every muscle and tissue in our bodies, but they’re all coordinated to the same rhythm by our brain. This is controlled by the suprachiasmatic nucleus, which is in the hypothalamus part of our brain. The circadian rhythm at its core is a balance between sleepiness and wakefulness, but it also helps with temperature regulation, hormone release and more. It is impacted by a range of factors, like caffeine intake, blue light exposure, and jet lag, but is affected by light exposure primarily.
Light and melatonin
In another part of the brain, the pineal gland controls melatonin production in response to the light intake where the retina processes light and sends the signal to the pineal gland, which, when a large amount of light is taken in, makes you more awake, and as the light decreases throughout the evening, melatonin is no longer suppressed and makes you feel tired, making most animals sleep during the night and awake during the day.
The stages of sleep
Sleep itself is split up into stages during the night, with four stages in each cycle, and many 70–120-minute cycles occurring every night. Firstly, the transition stage where your body is partly between sleep and wakefulness, and the muscles start to relax, then the light sleep stage occurs, where heart rate and breathing slow and core temperatures drop, and muscles relax even further. Eventually, you transition into stage 3: deep sleep, where the body relaxes further and there are slow brain waves. This stage is vital to muscle relaxation as well as memory and cognitive development. And finally, the REM stage, where your eyes move rapidly with the same amount of brain activity as though you were awake, breathing rate increases and the body becomes paralyzed to stop you from acting out your dreams.
Why do we need sleep?
Sleep is a fundamental part of every animal’s life, so why do we need it? Without it, the risk of many physical and mental health problems increases with poor quality sleep, like cardiovascular disease, depression, type 2 diabetes, and seizures, as sleep affects the production of vital hormones, therefore changing our moods and bodies. During sleep, more cytokines are produced, and the immune system is built, decreasing the likelihood of infection or illness, so it makes sense that humans need many hours of sleep a night. This is also to maintain ‘brain plasticity’, which is our brain’s ability to input and process information, without enough sleep, we cannot process the information from that day leading to poor memory and understanding, in addition to this, new research has shown that during sleep, waste products are removed from brain cells more effectively, also highlighting the benefits of sleep.
References:
https://www.sciencenewstoday.org/what-happens-when-you-sleep-the-biology-of-rest-and-recovery
https://www.nigms.nih.gov/education/fact-sheets/Pages/circadian-rhythms
Milly is Year 12 student from Cambridge who is currently taking part in the bronze award. Her main interests are Reading, Biology and Media. She aspires to become a doctor.
