What Happens To Your Body During Sleep?

Contrary to popular belief, sleep is not an optional luxury that you can skip out on or simply a habit. Just like eating — or breathing — sleep is a biological requirement of the body.

Sleep deprivation has been linked to a number of chronic diseases, so it’s important to get 7-9 hours of sleep each night.

It's also the crucial time when your brain and body conducts processes to repair itself and maintain optimal functionality (surely you've noticed how you feel after a night of no sleep).

It turns out that sleep is a highly organized, scientific process. Scientists use electroencephalography to study brain activity during sleep, which has led to the discovery of what’s known as the sleep architecture.

Sleep architecture divides sleep into four stages that people cycle through every night. Let’s take a look at these as well as several benefits of sleep!

The Sleep Cycle

The sleep cycle is regulated by the circadian rhythm, which in turn is driven by an area of the brain called the suprachiasmatic nucleus (SCN).

The SCN responds to reduced levels of light entering the eyes by releasing a hormone called epinephrine. Epinephrine travels to the pineal gland (a small structure located within the brain) and causes the release of melatonin, the sleep hormone.

There are two major patterns of sleep — rapid-eye-movement (REM) and non-REM. Together, they make up the four sleep stages.

Stage N1

This is the first stage of sleep and is characterized by non-REM sleep. During N1, you sleep lightly, and your heart rate, brain activity, and eye movements all slow down.

People spend around 7 minutes (or about 5% of their time) in N1 sleep each night.

Stage N2

During stage N2, you slip into deeper sleep. The pattern of the sleep is still non-REM, and your heart rate, muscles, and brain activity continue to slow down and relax.

However, numerous bursts of brain activity begin and these are known as sleep spindles and K complexes.

People spend most of their time — about 45% — in N2 sleep each night. Some people also grind their teeth during this stage, which is known as bruxism.

Stages N1 and N2 are the easiest to wake up from.

Stage N3

Stage N3 is the deepest non-REM sleep stage. This is where you enter deep sleep and your brain activity ebbs to the lowest point during the night. The heart and respiratory rate also fall to the lowest point.

Importantly, you need N3 sleep to feel fresh when you wake up. Your body performs restorative functions (like the repair of cells and tissues) during this stage.

Also, sleepwalking and bedwetting occurs during this stage so if you see someone sleepwalking, know that they’re in stage N3 sleep!

REM Sleep

During REM sleep, your brain activity accelerates (and its oxygen consumption increases). The heart rate and breathing also increase, and your eyes move quickly from side to side (hence the name of the stage).

While dreaming can occur during any sleep stage, it occurs most frequently during REM sleep. Luckily, your muscles are paralyzed during this stage to prevent you from reacting to dream content.

It’s believed that REM sleep helps the brain in-memory processing, making it important for learning.

People enter REM sleep every 90 minutes during the night and its duration increases in the second half of the sleep.

Why is sleep important?

We’ve seen how sleep is an organized process. But why do we need it? Let’s take a look at some key benefits of sleep.

Improved brain function

According to the brain plasticity theory, sleep is required for the brain to:

• Re-organize nerve cells
• Get rid of toxic waste products that accumulate throughout the day
• Convert short-term memories into long-term memories to facilitate learning
• Delete unwanted information to prevent cluttering

Keeping hunger in check

Hunger is regulated by two hormones. Ghrelin makes you feel hungry, while leptin promotes satiety.

When you’re sleep-deprived, the brain increases ghrelin production and suppresses leptin, making you feel hungry.

This increases caloric intake and unhealthy weight gain. This is why chronic sleep deprivation has been linked to complications of obesity like type 2 diabetes mellitus and metabolic syndrome.

Emotional stability

When you sleep, the areas of the brain that regulate emotions (like the amygdala, striatum, and medial prefrontal cortex) increase their activity.

This is thought to promote emotional well-being and provide emotional stability to the individual. When you’re sleep-deprived, emotional centers of the brain may start to overreact to stimuli, leading to increased stress and emotional lability.

Cell repair and growth

Scientists believe that sleep is essential for many restorative processes in the body. These include tissue growth, protein synthesis, and muscle repair.

Growth hormone is a hormone that promotes bone and muscle development in the body, and its levels are the highest right after you fall asleep. This is why it’s especially important for kids to get adequate sleep.

Strengthened immunity

The COVID-19 pandemic has sparked discussions on how to improve immunity. It turns out one simple way of achieving good immunity is to get good sleep.

During sleep, the body produces chemicals called cytokines. Cytokines coordinate and regulate the immune system, improving your ability to fight off germs. The body also produces numerous white blood cells and antibodies during sleep, both of which are important components of the immune system.

A word on insufficient sleep: Insomnia, restless leg syndrome, and sleep apnea are some conditions that can deprive you of sleep. You should know that chronic sleep deprivation is associated with:

• Increased blood pressure
• Increased stress hormone (cortisol) levels, which has numerous deleterious effects on the body
• Weight gain
• Increased risk of injury
• Increased risk of bone fractures in older adults
• Kidney, brain, and psychological problems

This is why it’s important to get adequate sleep each night. The ideal sleep duration for you will depend on your age, and you can read more about it here. But if you feel you’ve been getting inadequate sleep at night due to a medical condition, it’s important to consult a doctor for it.