Sleep is an important part of your daily routine – you spend about a third of your time doing it. Adequate sleep—and enough of it at the right time—is as essential to survival as food and water. Without sleep, you cannot create and maintain new neural pathways in the brain that help you learn and create new memories, and it becomes harder to focus and respond quickly without enough sleep.
Sleep is important for a number of brain functions, including how nerve cells (neurons) communicate with each other. In fact, your brain and body are extremely active when you sleep. Recent findings show that sleep plays an important role in eliminating toxins from your brain.
Everyone needs sleep. Sleep affects almost every tissue and system in the body—from the brain, heart, and lungs to metabolism, immune function, mood, and resistance to disease. Research shows that chronic lack of sleep or lack of sleep increases disorders such as high blood pressure, cardiovascular diseases, diabetes, depression and obesity. With the new methods that scientists have now discovered, it is clear that sleep is a complex and dynamic process that affects how you function.
Anatomy of sleep
Several structures within the brain are associated with sleep.
First, the hypothalamus, a peanut-sized structure deep in the brain, which contains a group of nerve cells that act as control centers affecting sleep and agitation. Inside the hypothalamus there is a section (SCN) that receives information about light directly from the eyes and controls its behavioral rhythm. Some people with SCN disorders experience sudden daytime sleepiness because they are unable to match their circadian rhythm with the light-dark cycle. Most blind people have this type of sensitivity and can change their sleep/wake cycle.
The brainstem communicates with the hypothalamus to control the transition between wakefulness and sleep. (Our brain includes structures known as pons, medulla, and midbrain.) The cells responsible for sleep in the hypothalamus and brain stem produce a magnetic chemical called GABA, which reduces the activity of excitable centers in the hypothalamus and brain stem. It becomes the brain. The brainstem (especially the pons and medulla) also plays an important role in REM sleep. Through it, the brain sends signals to reduce body movements during sleep.
The thalamus acts as a relay for information from the senses to the cerebral cortex (the covering of the brain that interprets and processes information from short-term and long-term memory). During most stages of sleep, the thalamus relaxes, allowing you to tune in to the outside world. But during REM sleep, the thalamus is active and is responsible for sending the brain images, sounds, and other sensations that fill our dreams.
The pineal gland, located in both hemispheres of the brain, receives signals from the SCN and increases the production of the hormone melatonin, and after the ambient light has dimmed, you can sleep. People who have lost an eye and cannot coordinate their natural sleep and sleep cycles using natural light can stabilize their sleep patterns by taking small amounts of melatonin at the same time. Scientists believe that the ups and downs of melatonin secretion over time are related to the adaptation of the body’s circadian rhythm to the external cycle of light and darkness.
The basal forebrain, near the front and bottom of the brain, causes sleep and wakefulness, while part of the midbrain acts as an excitatory system. The release of adenosine (a chemical produced from cellular energy consumption) from the basal cells of the forebrain and possibly other regions supports your sleep onset. Caffeine controls sleepiness by blocking the actions of adenosine. The amygdala, an almond-shaped structure involved in emotion processing, becomes increasingly active during REM sleep.
stages of sleep
There are two basic types of sleep: Rapid eye sleep (REM) and non-REM sleep, which has three different stages. Each is associated with specific brain waves and neural activity. In a typical night, you nap several times in all stages of non-REM and REM sleep, with the deepest REM periods experienced near the morning.
The first stage of non-REM sleep is the transition from wakefulness to sleep. During this short period (a few minutes) of relatively little sleep, your heart rate, breathing, and eye movements decrease, and muscles contract with occasional jerks. Your brainwaves tend to shift from fast, high-frequency daily patterns to slow waves.
The second stage of non-REM sleep is a period of light sleep experienced before deeper sleep. Your heart rate and breathing slow and your muscles relax even more than before. Your body temperature drops and eye movements stop. Brain wave activity slows down, but brain activity is accompanied by small spikes of electrical activity. Your sleep cycles are more frequent in this stage than in other stages.
Stage 3 non-REM sleep is the period of deep sleep that leaves you feeling refreshed in the morning. It occurs in long periods in the first half of the night. Heart rate and breathing reach their lowest levels during sleep. Your muscles are relaxed and you hardly wake up. Brain waves slow down during this period.
REM sleep first occurs about 90 minutes after falling asleep. Your eyes are moving fast. The frequency activity of the brain becomes closer to that which exists in wakefulness. Your breathing becomes faster and more irregular, and your heart rate and blood pressure increase to near-awake levels. Most of your dreams occur during REM sleep, although some can also occur during non-REM sleep. Your arm and leg muscles are temporarily paralyzed, preventing them from moving during sleep. As you get older, you spend less time in REM sleep. Memory consolidation most likely requires non-REM and REM sleep at the same time.
Mechanism of sleep
The two factors of circadian rhythm and homeostasis interact to regulate when you wake up and when you go to sleep.
Pregnancy rhythms guide a wide range of functions from daily fluctuations in wakefulness to body temperature, metabolism, and hormone release. They control your sleep time and make you sleepy at night and wake you up in the morning without an alarm. Your body’s biological clock, which is based on a roughly 24-hour day, controls most daily rhythms. Digital rhythms are synchronized with environmental cues (light, temperature) to the actual time of day, but persist even in the absence of cues.
Sleep homeostasis follows your need for sleep.
Factors that affect your need for sleep include medical conditions, medications, stress, sleep environment, and what you eat and drink. Exposure to light may have the greatest effect. Specialized cells in your retina process light and tell the brain whether it’s day or night and can start or delay our sleep-wake cycle. Exposure to light wakes us up.
Night shift workers fall asleep during the day and fall asleep with difficulty because the natural circadian rhythm is disrupted.