We spend on average 25 years of our lives sleeping. Our sleep affects our health on a daily basis and impacts heavily on our quality of life. We can even die without it, but after decades of study, scientists still don’t truly know why sleep is such an integral part of our lives.
What scientists do know is what happens to us physiologically when we put our heads down for the night. Our bodies and minds undergo some very strange processes during sleep that all help sort information, recover lost energy and repair damage. Let’s examine a typical night’s sleep.
Sleep and wakefulness are governed by your brain. Different brainwaves are produced during different stages of sleep. Before we venture into Dreamland, let’s look at what your brain output waves consist of - click on the brain and brainwaves to find out more about them:
Sleep can be broken down into two main categories:
Within these, there are five stages that we continuously cycle through during the night. We spend the vast majority of our time asleep in NREM – the deepest kind of sleep.
This is where you become drowsy, beginning to drift off to sleep. You can still be easily awakened at this point and your brain activity is still quite high – but your brainwaves are moving away from the Beta and into the Alpha spectrum, becoming more irregular than when fully awake and alert. Towards the end of this stage, your brainwaves become more amplified and feature more Theta waves.
While you can still be woken up easily at this stage, you have descended into a light NREM sleep. Your body is most prone to sleep twitches at this point, as you transition from a semi-waking state to light sleep. As you’re still semi-conscious, you can still be easily woken.
Your Theta brainwaves start to spike in what are called “sleep spindles” – bursts of activity lasting a second or so. At the end of this stage, K-complex waves are emitted by the brain and you become disengaged from your surroundings. Your heart and breathing rates stay the same, but your body temperature begins to drop (sleeping in a cooler room can help you get to sleep).
In Stage 3, bodily movement is reduced as your muscles begin to relax. As this stage progresses, you become more and more difficult to wake up. Your body temperature lowers further and your brainwaves stop producing sleep spindles. You’re about to enter the deepest sleep when your brainwaves transition into Delta waves – high-amplitude, low-frequency waves where the brain is incredibly active; more so than when you’re awake. Females across most species, not just humans, have been shown to have higher Delta wave activity than males.
This is the deepest stage of sleep you can enter. You are extremely difficult to wake as your brain output consists almost exclusively of Delta waves. Your blood pressure falls and blood flow to your muscles reaches its peak. Your heart rate and breathing slow down. If you’re a snorer, this is when snoring occurs.
This stage is one of the most important: it’s where cell and tissue repair takes place and your immune system is at its strongest. Hormones are released to promote growth and muscle repair. Energy is restored to the brain and body.