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Brain Basics: Understanding Sleep
Every executive I spoke to, when asked about how it all fits together, cites this desire to get you whatever you want in the shortest window possible. Give me one good reason why I should stay. The documents describe a system that would seem to extend the AmazonFresh grocery service: Using a companion app, data from some devices can be synced to a smartphone or tablet, or uploaded to a PC. How are the somatic and autonomic nervous systems similar? Why didn't I think of that?

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Sleep is a complex and dynamic process that affects how you function in ways scientists are now beginning to understand. This booklet describes how your need for sleep is regulated and what happens in the brain during sleep.

The hypothalamus , a peanut-sized structure deep inside the brain, contains groups of nerve cells that act as control centers affecting sleep and arousal. Within the hypothalamus is the suprachiasmatic nucleus SCN — clusters of thousands of cells that receive information about light exposure directly from the eyes and control your behavioral rhythm. Some people with damage to the SCN sleep erratically throughout the day because they are not able to match their circadian rhythms with the light-dark cycle.

The brain stem , at the base of the brain, communicates with the hypothalamus to control the transitions between wake and sleep. The brain stem includes structures called the pons, medulla, and midbrain. Sleep-promoting cells within the hypothalamus and the brain stem produce a brain chemical called GABA , which acts to reduce the activity of arousal centers in the hypothalamus and the brain stem. 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- to long-term memory.

During most stages of sleep, the thalamus becomes quiet, letting you tune out the external world. But during REM sleep, the thalamus is active, sending the cortex images, sounds, and other sensations that fill our dreams. People who have lost their sight and cannot coordinate their natural wake-sleep cycle using natural light can stabilize their sleep patterns by taking small amounts of melatonin at the same time each day.

The basal forebrain , near the front and bottom of the brain, also promotes sleep and wakefulness, while part of the midbrain acts as an arousal system. Release of adenosine a chemical by-product of cellular energy consumption from cells in the basal forebrain and probably other regions supports your sleep drive.

Caffeine counteracts sleepiness by blocking the actions of adenosine. The amygdala , an almond-shaped structure involved in processing emotions, becomes increasingly active during REM sleep.

There are two basic types of sleep: Each is linked to specific brain waves and neuronal activity. Stage 1 non-REM sleep is the changeover from wakefulness to sleep.

During this short period lasting several minutes of relatively light sleep, your heartbeat, breathing, and eye movements slow, and your muscles relax with occasional twitches. Your brain waves begin to slow from their daytime wakefulness patterns. Stage 2 non-REM sleep is a period of light sleep before you enter deeper sleep. Your heartbeat and breathing slow, and muscles relax even further. Your body temperature drops and eye movements stop. Brain wave activity slows but is marked by brief bursts of electrical activity.

You spend more of your repeated sleep cycles in stage 2 sleep than in other sleep stages. Stage 3 non-REM sleep is the period of deep sleep that you need to feel refreshed in the morning. It occurs in longer periods during the first half of the night. Your heartbeat and breathing slow to their lowest levels during sleep. Your muscles are relaxed and it may be difficult to awaken you. Brain waves become even slower. REM sleep first occurs about 90 minutes after falling asleep. Your eyes move rapidly from side to side behind closed eyelids.

Mixed frequency brain wave activity becomes closer to that seen in wakefulness. Your breathing becomes faster and irregular, and your heart rate and blood pressure increase to near waking levels. Your arm and leg muscles become temporarily paralyzed, which prevents you from acting out your dreams. As you age, you sleep less of your time in REM sleep. Two internal biological mechanisms —circadian rhythm and homeostasis—work together to regulate when you are awake and sleep.

Circadian rhythms direct a wide variety of functions from daily fluctuations in wakefulness to body temperature, metabolism, and the release of hormones. They control your timing of sleep and cause you to be sleepy at night and your tendency to wake in the morning without an alarm. Circadian rhythms synchronize with environmental cues light, temperature about the actual time of day, but they continue even in the absence of cues.

Sleep-wake homeostasis keeps track of your need for sleep. The homeostatic sleep drive reminds the body to sleep after a certain time and regulates sleep intensity.

This sleep drive gets stronger every hour you are awake and causes you to sleep longer and more deeply after a period of sleep deprivation. Factors that influence your sleep-wake needs include medical conditions, medications, stress, sleep environment, and what you eat and drink.

Perhaps the greatest influence is the exposure to light. Specialized cells in the retinas of your eyes process light and tell the brain whether it is day or night and can advance or delay our sleep-wake cycle. Exposure to light can make it difficult to fall asleep and return to sleep when awakened.

Night shift workers often have trouble falling asleep when they go to bed, and also have trouble staying awake at work because their natural circadian rhythm and sleep-wake cycle is disrupted. In the case of jet lag, circadian rhythms become out of sync with the time of day when people fly to a different time zone, creating a mismatch between their internal clock and the actual clock.

Your need for sleep and your sleep patterns change as you age, but this varies significantly across individuals of the same age. Babies initially sleep as much as 16 to 18 hours per day, which may boost growth and development especially of the brain.

School-age children and teens on average need about 9. Most adults need hours of sleep a night, but after age 60, nighttime sleep tends to be shorter, lighter, and interrupted by multiple awakenings. Elderly people are also more likely to take medications that interfere with sleep. They worked really hard. Give me one good reason why I should stay.

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I know why he did it. It's easy to see why she fell in love with him. He's a very good player. That's why he made the team. The reason why they succeeded is obvious. They worked really hard. Give me one good reason why I should stay. Why is the Sky Blue? The blue color of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air. However, much of the shorter wavelength light is absorbed by the gas molecules. for what cause or reason: I don't know why he is leaving. for which; on account of which (usually after reason to introduce a relative clause): the reason why he refused to go. the reason for which: That is why he returned.