A Tour of Snooze Land

Sleep your way to  good health!

 

“I love sleep. My life has the tendency to fall apart when I’m awake, you know?”
Ernest Hemingway

Sleep is a naturally recurring state of mind and body characterized by altered consciousness, relatively inhibited sensory activity, inhibition of nearly all voluntary muscles, and reduced interactions with surroundings. It is distinguished from wakefulness by a decreased ability to react to stimuli.

 

Stages of sleeping

Human sleep occurs in cycles. Each cycle is approximately 90 minutes. Each cycle is divided to Non-REM and REM. Normally in that order and usually four or five of them per night. Although each cycle consists of Non-REM and REM, they are not of the same duration. Non-REM takes more time.

1. Non-REM:

It stands for Non Rapid Eye Movement phase.As an organism falls asleep, the activity of its body slows down. Body temperature, heart rate, breathing rate, and energy use all decrease. Brain activity get slower. It constitutes ~80% of all sleep in humans.

Light sleep is the beginning of Non-REM. It is 5–10% of total sleep in adults. This is a stage of sleep that usually occurs between sleep and wakefulness. The muscles are active, and the eyes roll slowly, opening and closing moderately. The body loses some muscle tone and most conscious awareness of the external environment.

Deep sleep follows. It’s about 15–25% of total sleep in adults. The sleeper is less responsive to the environment; many environmental stimuli no longer produce any reactions. Deep sleep is thought to be the most restful form of sleep, the phase which most relieves subjective feelings of sleepiness and restores the body.

This is also the stage in which parasomnias such as night terrors, nocturnal enuresis, sleepwalking, and sleep talking occurs.

2. REM:

It stands for Rapid Eye Movement sleep. It is characterized by random movement of the eyes. In this stage, eyes move rapidly under the eyelids. It constitutes 20–25% of total sleep in adults.In this stage most muscles are paralyzed, and heart rate, breathing and body temperature become irregular.

This stage is also referred to as paradoxical sleep because the sleeper is very difficult to awake, although his vital signs indicate arousal and oxygen consumption by the brain is higher than when the sleeper is awake.

This is the stage when dreams occur. Functional paralysis may be necessary to protect the body from self-damage through physically acting out scenes from the often-vivid dreams that occur during this stage.

The function of REM sleep is uncertain but it’s thought to be importantfor memory and learning complex tasks.

A newborn baby spends almost 9 hours a day just in REM sleep. By the age of five or so, only slightly over two hours is spent in REM.

3. Awakening:

Awakening means the end of sleep. Sleepers typically awaken soon after the end of a REM phase or sometimes in the middle of REM. Internal biological clock, along with successful reduction of body sleep need, typically bring about awakening and the end of the sleep episode.

What Makes You Sleep?

You have an internal biological clock that controls when you’re awake and when your body is ready for sleep.

The body clock typically has a 24-hour repeating rhythm (called the circadian rhythm). Two processes interact to control this rhythm:

The first is a pressure to sleep that builds with every hour that you’re awake. This drive for sleep reaches a peak in the evening, when most people fall asleep.A compound called adenosine seems to be one factor linked to this drive for sleep. While you’re awake, the level of adenosine in your brain continues to rise. The increasing level of this compound signals a shift toward sleep. While you sleep, your body breaks down adenosine.

The second process involves your internal body clock. This clock is in sync with certain cues in the environment. Light, darkness, and other cues help determine when you feel awake and when you feel drowsy.

For example, light signals received through your eyes tell a special area in your brain that it is daytime. This area of your brain helps align your body clock with periods of the day and night.

Your body releases chemicals in a daily rhythm, which your body clock controls. When it gets dark, your body releases a hormone called melatonin .Melatonin signals your body that it’s time to prepare for sleep, and it helps you feel drowsy.

As the sun rises, your body releases cortisol. This hormone naturally prepares your body to wake up.

Exposure to bright artificial light in the late evening can disrupt this process, making it hard to fall asleep. Examples of bright artificial light include the light from a TV screen, computer screen, or a very bright alarm clock.

The rhythm and timing of the body clock change with age. Teens fall asleep later at night than younger children and adults. One reason for this is because melatonin is released and peaks later in the 24-hour cycle for teens. As a result, it’s natural for many teens to prefer later bedtimes at night and sleep later in the morning than adults. 

Modern humans often find themselves desynchronized from their internal Biological clock, due to the requirements of work (especially night shifts), long-distance travel, and the influence of widespread indoor lighting.

We will talk about sleep debt soon. Stay tuned!

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