How the Brain Works: The Physiology of Sleep

The human body has certain requirements for good health, including adequate amounts of water, food, and sleep. Without these, the human body cannot thrive. In today’s busy world, it is often easier to sip a drink or grab a bite to eat than it is to get several hours of sleep. But a lack of adequate sleep deprives a person of the restorative rest that their brain and body requires.

People spend approximately one-third of their lives sleeping. When there is a disruption in the amount or quality of sleep that they receive, it can have a negative impact on their health or quality of life. That’s because a lot happens during sleeping hours. The brain uses this time to flush out toxins through a waste management system known as the glymphatic system. Sleeping also helps with memory and enables the brain to process what’s learned during waking hours.

When people get a good night’s sleep, they can think clearly and concentrate during the day. A lack of sleep can cause an inability to concentrate and also increase one’s risk of disease and illness, such as diabetes and high blood pressure.

To properly appreciate the need for sleep and all that it accomplishes, it helps to understand the basics of how the brain and sleep work.

Anatomy of Sleep

There are structures in the brain that make sleeping possible. One of these structures is the hypothalamus, which is located deep inside the brain. This structure is small, roughly the size of a peanut, but it plays an important role in sleep. Within the hypothalamus are a group of nerve cells that affect sleep and arousal.

Arousal signals from the hypothalamus encourage wakefulness, while the shutting down of arousal signals helps promote sleep. In the anterior hypothalamus is the suprachiasmatic nucleus (SCN). Within it is a cluster of neurons that are often referred to as the “master clock.” The SCN is sensitive to light, as it is in the optic chiasm. This sensitivity enables it to send signals that control behavioral or circadian rhythms.

At the base of the brain is the brain stem. The brain stem and the hypothalamus aid in the transition from wakefulness to sleep when their cells produce GABA, a chemical that reduces arousal and slows brain activity to promote sleep. During sleep, the brain stem also sends out signals to muscles in the body. These signals cause muscles to relax so that dreamers aren’t physically reacting to their dreams.

At the middle of the brain, above the brain stem, is the thalamus. This structure’s job is to relay information coming from one’s senses and movement to the brain. The thalamus acts as a relay station that passes information to the correct part of one’s cerebral cortex for processing. During rapid eye movement (REM) sleep, the thalamus provides the cerebral cortex with information, such as visuals and sounds, for dreams.

The pineal gland is a tiny endocrine gland shaped like a pine cone. It secretes a hormone called melatonin that helps to synchronize the circadian rhythm. The amount of hormone that it produces correlates to the amount of information about daylight and darkness that it receives. Signals from SCN cause the pineal gland to increase the amount of melatonin that it produces when it’s dark, which helps people fall asleep at night.

At the front of the brain, near the bottom, is the basal forebrain, which is important to the sleep-wakefulness cycle. The basal forebrain releases a neurotransmitter called adenosine. This chemical is produced and builds up as people expend energy. An increase in adenosine equals a greater need to sleep.

The amygdala is a tiny brain structure that processes powerful emotions, such as anger or pleasure. When a person is sleeping, their amygdala is most active during the REM sleep cycle

Sleep Stages and Mechanisms

There are four stages of sleep. The first three stages fall under non-REM sleep, and the fourth stage is REM sleep. Throughout the night, people cycle through these stages several times. Stage 1 lasts for roughly 5 to 10 minutes and is the transition period between being awake and asleep. Stage 2 lasts for approximately 20 minutes.

While in this stage, one’s breathing and heart rate slow down and their temperature drops. During Stage 3 of non-REM sleep, a person gets their deepest and most restful sleep. Their muscles become more relaxed, and their blood pressure drops and breathing slows. Some dreaming may also occur at this time.

After around 90 minutes of sleep, the fourth and final stage, REM sleep, occurs. REM sleep is when people have dreams. During this time, brain activity increases, the eyes move back and forth rapidly, and one’s blood pressure becomes close to its normal waking rate. While in REM sleep, the body’s muscles become temporarily immobile. REM sleep lasts for 10 to 60 minutes and lasts longer closest to the morning. This stage is important for memory and learning.

Two mechanisms, circadian rhythm and sleep-wake homeostasis, regulate sleep. The circadian rhythm is part of one’s biological clock. It is a system that not only regulates sleep but also a range of bodily functions, such as metabolism, over a 24-hour cycle.

Light and temperature influence the circadian rhythm and the fluctuations associated with sleepiness or wakefulness over the course of the day. The other sleep process, sleep-wake homeostasis, regulates the need to go to sleep. This causes one to become increasingly tired the longer that they are awake. It also causes people to sleep longer if they haven’t gotten enough sleep.

When either of these natural processes is disrupted, it can negatively affect a person’s ability to sleep. Some things that can interfere with these processes include working late hours, brain injury, flying across time zones, drug use, or frequently changing one’s bedtime.

Dreaming and Sleep Tracking

Dreams are stories that the brain creates during sleep. They can be colorful and often can cause intense emotions such as happiness, fear, or even sadness. People can dream in all stages of sleep. However, the most intense dreams occur when the brain is most active, which is during REM sleep.

There are a lot of theories about dreams and whether they have a purpose. While some scientists believe that there is no benefit to dreaming, many others believe that dreams help process memories, help people learn, and aid in problem-solving. Dreams are also thought to have a connection with creativity.

The Role of Genes and Neurotransmitters

Genes and chemical signals are important parts of any discussion about sleep. Chemicals called neurotransmitters play a big role in one’s ability to sleep or stay awake.

Besides GABA, melatonin, and adenosine, other neurotransmitters that are associated with the sleep-wake cycle include glutamate, acetylcholine, norepinephrine, dopamine, histamine, and serotonin. Histamine regulates sleep, but too much can cause insomnia. Glutamate regulates REM sleep and wakefulness.

Genes play a part in several aspects of sleep, and they can also make people more susceptible to sleep disorders. Some genes affect one’s circadian rhythm, while others can put people at higher risk of developing conditions such as narcolepsy, chronic insomnia, advanced sleep-phase syndrome, and restless leg syndrome.

How Much Sleep Do You Need?

The amount of sleep a person needs can vary depending on the individual and their age. According to the Centers for Disease Control and Prevention, adults 18 to 60 years old should get 7 or more hours of sleep a night. Between 7 and 9 hours a night is the recommendation for adults 61 to 64 years old, and 7 to 8 hours is adequate for people 65 years or older.

For younger people, the recommended number of hours of sleep per night is greater. The American Academy of Sleep Medicine (AASM) recommends 12 to 16 hours for infants between 4 to 12 months, 11 to 14 hours of sleep for 1-to-2-year-olds, and 10 to 13 hours for preschoolers ages 3 to 5 years old. Kids between the ages of 6 and 12 years old should get between 9 to 12 hours of sleep per 24 hours, while teens should get anywhere between 8 and 10 hours.

Tips for Getting a Good Night’s Sleep

Getting enough restful sleep can be an issue for some people. Fortunately, there are things that a person can do to sleep better at night, like avoiding caffeine or other stimulating drinks and not eating for several hours before bedtime. Creating a sleep schedule is also an important step. This means setting one’s clock to a specific time to go to bed at night and wake up every day. Sticking to a sleep schedule, even on the weekends, will establish a routine that can make it easier to sleep.

Sleep routines are also important. Night routines are relaxing activities, such as taking a bath, that help people wind down at night. This nightly routine becomes a signal to the body and mind that it’s time to settle down and go to sleep. Creating an atmosphere that is dark, quiet, and relaxing will also make it easier to fall asleep at night, as will removing electronic devices, including cellphones and televisions.

More Information

About Derek Hales

Derek Hales is the Founder and Editor-in-Chief of NapLab.com. He has been featured in Fast Company, Reader's Digest, Business Insider, Realtor.com, Huffington Post, Washington Post, AskMen, and She Knows. Derek has personally tested over 320+ mattresses and hundreds of pillows, sheets, beds, and other sleep products.