We often tend to think of sleep as a passive process where your body shuts down for you to get some rest. But there is a lot going on in your body and your brain while you are sleeping. Have you ever asked yourself why we need sleep and what happens in your body while you are sleeping?
Sleep is important for our physical and mental health. Your brain and body recover for the day and get ready for next day. Learning is reinforced and dreaming during REM sleep is important for memory and learning new things. Growth hormones is secreted in the deep sleep stage and this helps muscles and other parts of body to recover from wear and tear that occurred during the day and helps the body to heal from illness. Stress hormones levels are lower in sleep and this lowers blood pressure and allows heart and blood vessels to relax.
THE SCIENCE BEHIND SLEEP:
There is an internal body clock that controls our sleep and wake cycles over a 24 hour period in a circadian rhythm. The sleep-wake center of the brain is located in a special region of the brain known as the hypothalamus, and more precisely, by a small group of cells in the hypothalamus known as the Suprachiasmatic Nucleus. The hypothalamus also hosts the regulatory centers for body temperature and hunger. The circadian clock is regulated by external stimuli, mainly light and temperature. When light dims in the evening and the temperature drops, the brain is stimulated to secrete melatonin, a hormone that induces drowsiness and prepares the body for sleep. At the dawn of day with sunlight, and rising temperature in the morning, the body releases cortisol which leads to alertness and keeps you awake during the day. As the day progresses, the level of cortisol decreases and levels of another molecule called Adenosine increases, causing a decrease in level of alertness which progressively increases as you approach bedtime. This is referred to as the homeostatic sleep drive.
Stages of Sleep:
Sleep is a well-organized process in which you go through one sleep stage to another, completing several sleep cycles throughout the night. There are 4 sleep stages: Stage 1 to 3 are Non-REM stages and Stage 4 is REM stage sleep. Based on the duration of sleep, you can go through 4 to 6 sleep cycles. Each sleep cycle is composed of the different stages of sleep and can last from 80 to 120 minutes.
Stage 1: Also known as stage N1: This marks the transition from wakefulness into sleep and is also the first stage of light sleep. You become drowsy but are still semi-aware of your surroundings and are starting to lose this awareness. Your muscles begin to relax, your breathing and heart rate slow down. Eye movements are still present. This stage us usually brief, lasting less than 5 minutes.
Stage 2: Also known as Stage N2: You continue to lose awareness of your surrounding and are getting deeper into sleep, with your heart rate, breathing slowing down further and your muscles even more relaxed. Eye movements cease and your body temperature drops. This is usually the longest of all 4 stages and can last up to several hours.
Stage N3: Also known as N3, “Slow wave sleep” or “deep sleep”. In this stage, you have completely lost awareness of your environment. Your heart rate, breathing, blood pressure and brain activity are all at the lowest levels and your muscles are at their most relaxed state. Your body experiences the lowest blood pressure of the day (“Nocturnal deep in blood pressure”) which is very important for your cardiovascular health. Growth hormone is also secreted in this stage which helps in repair and regeneration of the body. Young children spend about 50%of their total sleep time in this stage. This stage is usually longer in the first half of the night but decreases as you progress into subsequent sleep cycles.
Stage 4: REM sleep: REM stands for Rapid Eye Movement and as the name suggests, your eyes are moving quickly under your shut eye lids. You have vivid dreams during REM sleep and your skeletal muscles are paralyzed, an unconscious protective mechanism to prevent you from acting out your dreams. Your brain becomes very active and your heart rate, breathing rate and blood pressure increase. It is thought than REM sleep plays an important role in memory, learning and creative thinking. REM sleep usually increases in intensity and frequency as the night progresses.
