What is sleep? It’s funny how sometimes we don’t know how the processes or technologies upon which we rely most — photosynthesis, computers, cars, our sleep cycles — actually work. And in order to know how something works, we need to know what it is. Sleep is an extremely important aspect of our lives that can mean the difference between a long, healthy, happy life and a shorter, ailing, depressed experience of life.
According to the National Institute of Neurological Disorders and Stroke: “Everyone needs sleep, but its biological purpose remains a mystery. Sleep affects almost every type of tissue and system in the body – from the brain, heart, and lungs to metabolism, immune function, mood, and disease resistance. Research shows that a chronic lack of sleep, or getting poor quality sleep, increases the risk of disorders including high blood pressure, cardiovascular disease, diabetes, depression, and obesity.”
More and better sleep correlates to a longer and better quality of life. When we fully appreciate the importance of sleep in our lives, it becomes clear that maybe it would be beneficial to know a thing or about what it actually is, and how it actually works. So, what is sleep? Let’s find out.
What is sleep?
The chemical breakdown
What physical and mental occurrences signal to us that this is sleep? According to the American Sleep Association, nerve-signaling chemicals called neurotransmitters control whether we are in a sleeping or waking phase by acting on and/or interacting with different groups of nerve cells — neurons — in the brain. Brainstem neurons, which connect the brain and spinal cord, produce neurotransmitters like serotonin and norepinephrine. These neurotransmitters ensure some parts of the brain are kept active while we’re awake. Other neurons located at the base of the brain start to signal when we begin to fall asleep. These neurons actually “flip off” the switches that keep are working to keep us awake. Studies also link the build up of a chemical called adenosine in our blood to drowsiness. Adenosine builds up during our waking hours to eventually make us feel tired, and then the chemical gradually breaks down while we sleep.
What happens when we sleep?
The sleep stages breakdown
Once those neurons at the base of our brain have switched off our neurotransmitter switches for being “awake,” and we’re now “asleep,” what’s happening in our brain during sleep? Well, it’s going through what science has divided into four vital stages of sleep. Watch this video breakdown of the four sleep stages and check out our written summary of the video and its explanation of sleep stages, below.
Put simply: The 4 stages of sleep
Stage 1: During stage 1 sleep, the brain reduces alpha waves and increases theta waves. Our eye movements also slow down. This is a very light stage of sleep. People in stage 1 sleep can be woken fairly easily.
Stage 2: We spend half our sleep time in this phase. Spindles — brief increases in brain wave frequency — characterize stage 2 sleep. This stage of sleep is specifically connected to our ability to absorb new learning. The density of these spindles denotes the amount of new learning we’re taking in. If you’re looking for a quick alertness boost in your day, sleep experts suggest taking a 10 to 20 minute power nap. This means grabbing a quick sleep that pretty much only makes it into stages 1 and 2 of sleep.
Stage 3: This stage is the beginning of deep sleep. In deep sleep, the brain begins producing slower delta waves. At this stage of sleep, it’s much harder to be awakened.
REM Sleep: Adults spend about 20 percent of sleep time in this last stage of sleep. Conversely, infants spend about 50 percent of their sleep time in REM. (The amount of REM sleep we need/engage in gradually decreases as we age). During REM sleep, our eyes move quickly in different directions. Meanwhile, our muscles become paralyzed, our breathing and heart rate become erratic, and vivid dreams can occur.
These four stages of sleep progress in a cycle as we’re sleeping and repeat themselves. Each stage has its vital role to play in keeping our brain and body healthy.
For more information about what sleep is, and about the four stages of sleep, click here.