What Happens During Sleep | OtterKnow Kids Encyclopedia

Your Body Is Busy While You Sleep

Even though you look perfectly still while you are sleeping, your body is very busy on the inside. Your heart keeps pumping blood, your lungs keep breathing, and your digestive system keeps processing food. But sleep is also the time when special processes kick in that cannot happen as well while you are awake. Growth hormones are released, your immune system is strengthened, and your brain actively sorts through the memories and experiences from the day. Sleep is far from doing nothing, as it is one of the most productive times for your body.

Sleep Comes in 90-Minute Cycles

When you fall asleep, your brain does not just shut off for the night. Instead, it moves through a repeating pattern of sleep stages that lasts about 90 minutes from start to finish. Each time you complete one of these cycles, your brain starts the pattern over again. On a typical night, you go through 4 to 5 complete sleep cycles. Each cycle contains two main types of sleep: NREM (non-rapid eye movement) sleep and REM (rapid eye movement) sleep, and each type does different jobs for your body and brain.

Stages of NREM Sleep

NREM sleep has three stages, and each one takes you deeper into sleep. Stage 1 is very light sleep, when you are just drifting off and can be easily awakened by a small noise. Stage 2 is where your heart rate slows down and your body temperature drops as your body prepares for deeper rest. Stages 3 and 4, often grouped together as deep sleep or slow-wave sleep, are the most restorative stages. During deep sleep, your body releases growth hormone, repairs tissues, and strengthens your immune system so you can fight off illness.

REM Sleep and Dreaming

REM sleep is one of the most active stages of the sleep cycle. During REM, your brain becomes highly active, almost as active as when you are fully awake, and this is when most of your vivid dreaming takes place. Your eyes move quickly back and forth beneath your closed eyelids, which is how this stage got its name. REM sleep is crucial for processing emotions, consolidating memories, and even boosting creativity. To keep you from acting out your dreams, your brain temporarily paralyzes most of your voluntary muscles during this stage.

The Brain’s Cleaning Crew

One of the most important discoveries about sleep in recent years involves the glymphatic system, which was identified by scientists in 2012. This system is your brain’s waste-clearance network, and it becomes about 60% more active during sleep. While you rest, cerebrospinal fluid flows through your brain tissue, washing away toxic waste products that accumulated during the day. Among the waste products cleared are proteins that have been linked to Alzheimer’s disease, a condition that causes memory loss in older adults. This cleaning process is one of the strongest reasons scientists believe sleep is not optional.

Deep Sleep Happens First, REM Comes Later

The balance between deep sleep and REM sleep shifts throughout the night in an interesting way. During the first half of the night, your sleep cycles contain more deep sleep, which is when most physical repair and growth happen. As the night goes on, each cycle contains less deep sleep and more REM sleep. By the early morning hours, your sleep cycles are dominated by REM, which is crucial for memory and emotional health. This is why cutting your sleep short by even an hour or two means you lose the most REM sleep, which can affect your mood and ability to learn.

Your Heart and Muscles Get a Rest

Sleep gives your cardiovascular system, which includes your heart and blood vessels, a much-needed break. During NREM sleep, your heart rate slows down and your blood pressure drops, giving your heart and blood vessels time to recover from the demands of the day. Your muscles also relax deeply during sleep, which allows them to repair tiny tears caused by physical activity. Athletes who get enough sleep recover faster and perform better than those who cut their sleep short. Even if you are not an athlete, your body still needs this nightly repair time.

Sleep Strengthens Your Immune System

Your immune system, which is your body’s defense against germs, bacteria, and viruses, does some of its best work while you sleep. During deep sleep, your body produces proteins called cytokines that help fight infection and inflammation. Studies have shown that people who sleep fewer than 7 hours per night are nearly three times more likely to catch a cold compared to those who sleep 8 hours or more. This is why doctors always recommend getting plenty of rest when you are feeling under the weather. Your body is using sleep as its most powerful weapon against illness.