What Happens When You Sleep?
As you sleep, your brain works to physically repair your body. In the process, your brain also flushes out waste that accumulates during your waking hours that may contribute to neurodegenerative diseases.
As this activity happens, your brain cycles through four stages of sleep multiple times a night. The first three stages of sleep are considered non-rapid eye movement (REM) sleep, and the fourth is REM sleep. Each stage of sleep is associated with certain brain wave patterns and physical activities:
Stage 1: This non-REM sleep lasts several minutes as you transition from being awake to falling asleep. Your heartbeat, breath, eye movements, and brain waves begin slowing down and your muscles relax.
Stage 2: The second stage is also non-REM sleep. Over the course of a night, you spend more time in this stage than other stages. During this stage of light sleep, you experience a lower body temperature and more relaxed muscles. Your heart and breath slow even more.
Stage 3: This stage of non-REM sleep is known as deep sleep. In this stage, your heart and breath reach their slowest rates. Your brain waves slow further, and it is difficult to wake you up. In the first half of the night, this stage is longer. In later cycles, it becomes shorter.
Stage 4: This stage is REM sleep. About 90 minutes after you first fall asleep, REM sleep begins. During REM, your breath and heart rate speed up. Your eyes move rapidly, hence the name of this stage. A majority of dreams occur during REM sleep. Your brain temporarily paralyzes your muscles, so you do not act out those dreams and hurt yourself.
What Is a Circadian Rhythm?
Circadian rhythms are internal cycles that run on a roughly 24-hour schedule, much like the earth’s rotation. Circadian rhythms originate in a part of the brain called the suprachiasmatic nucleus, found in the hypothalamus. These rhythms are most known for regulating your sleep-wake cycle, but they also regulate other important biological processes, such as your core body temperature, appetite, and hormone levels.
Sunlight entrains your circadian rhythm, impacting when you want to sleep and when you want to be awake.
When you are exposed to less light, such as in the evening, your melatonin levels rise and you feel sleepy. When you are exposed to more light, melatonin falls and cortisol rises, so you feel alert and awake.
Why Is Sleep So Important?
Sleep is as essential to our survival and wellbeing as food and water are. Sleep impacts nearly every aspect of the body, affecting the brain, heart, and lungs, as well as metabolism, mood, and immune system.
Physical, emotional, and mental health all depend, in part, on good sleep … READ MORE.