What is sleep?

Sleep is a physiological behavior that is common in all animal species. It forms around one third of a human life. It is not known clearly the exact functions of sleep but it seems to be essential for survival as prolonged sleep deprivation leads to severe physical impairment followed by cognitive loss and eventually death.

Sleep is a state where awareness to environmental stimuli is reduced. Sleep is different from states of coma, hibernation and death by the fact that it can be rapidly reversed.

Detailed definition of sleep
Nerve-signaling chemicals called neurotransmitters control whether we are asleep or awake by acting on different groups of nerve cells, or neurons, in the brain. Neurons in the brainstem, which connects the brain with the spinal cord, produce neurotransmitters such as serotonin and norepinephrine that keep some parts of the brain active while we are awake. Other neurons at the base of the brain begin signaling when we fall asleep. These neurons appear to “switch off” the signals that keep us awake. Research also suggests that a chemical called adenosine builds up in our blood while we are awake and causes drowsiness. This chemical gradually breaks down while we sleep. These all process takes place in several steps or stages.

Phases of sleep

Like most other mammals, humans also show two types of sleep:-

• rapid eye movement (REM)
• non-rapid eye movement (NREM) sleep
  Both these types of sleep have distinct features when evaluated using electroencephalogram or EEG.

EEG monitors the brain activities and electrical impulses within the brain during awake state and during sleep. REM and NREM sleep also differ from each other in terms of physical characteristics.

For example, during REM sleep the frequent bursts of eye movement activity occur. During REM sleep the EEG shows patterns similar to those when the person is awake. Thus it is a paradoxical state of sleep when the brain appears to be awake in terms of EEG but the individual is in deep sleep.

During NREM sleep there is decreased activation of the EEG. This is also called orthodox sleep. The brain appears to be calm.

Stages of sleep

During sleep, we usually pass through five phases: stages 1, 2, 3, 4, and REM (rapid eye movement) sleep. These stages of sleep progress in a cycle from stage 1 to REM sleep, then the cycle starts over again with stage 1. Children and adults spend almost 50 percent of their total sleep time in stage 2 sleep, about 20 percent in REM sleep, and the remaining 30 percent in the other stages. Infants, by contrast, spend about half of their sleep time in REM sleep.

Stage 1 Sleep
During stage 1, which is light sleep, we drift in and out of sleep and can be awoken easily. Our eyes move very slowly and muscle activity slows. People awakened from stage 1 sleep often remember fragmented visual images. Many also experience sudden muscle contractions called hypnic myoclonia or hypnic jerks, often preceded by a sensation of starting to fall. These sudden movements are similar to the “jump” we make when startled.

Stage 2 Sleep
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 and Stage 4 Sleep
In stage 3, extremely slow brain waves called delta waves begin to appear, interspersed with smaller, faster waves. By stage 4, the brain produces delta waves almost exclusively. It is very difficult to wake someone during stages 3 and 4, which together are called deep sleep. There is no eye movement or muscle activity. People awakened during deep sleep do not adjust immediately and often feel groggy and disoriented for several minutes after they wake up. Some children experience bedwetting, night terrors, or sleepwalking during deep sleep.

REM Sleep
When we switch into REM sleep, our breathing becomes more rapid, irregular, and shallow, our eyes jerk rapidly in various directions, and our limb muscles become temporarily paralyzed during sleep. Our heart rate increases, our blood pressure rises, and males develop penile erections. When people wake up during REM sleep, they often describe bizarre and illogical tales also known as dreams.

The first REM sleep period usually occurs about 70 to 90 minutes after we fall asleep. A complete sleep cycle takes 90 to 110 minutes on average. The first sleep cycles each night contain relatively short REM periods and long periods of deep sleep. As the night progresses, REM sleep periods increase in length while deep sleep decreases. By morning, people spend nearly all their sleep time in stages 1, 2, and REM.

The purpose of sleep

Scientists still haven’t pinpointed a succinct reason why animals need to sleep every night. However, based on research and monitoring the brains of sleeping humans, they have some ideas. Among its many functions, sleep:

• Offers the body a chance to recover from wear and tear of daily life.
  Many researchers have suggested the restorative effects of sleeping. This doesn’t just mean that the body rests during sleep—rather, the cells busily regenerate themselves and the body temperature, heart rate, and breathing drop in order to conserve energy.
• Facilitates learning & memory.
  Not only do you need rest to sustain the attention and concentration necessary to learn new tasks, but according to Harvard’s Division of Sleep Medicine, sleep is a time for the brain to consolidate memories, which makes learning new things easier. People who sleep after learning how to play a video game generally perform much better in the game later than those who stay awake. Even more intriguingly, a recent study in Natural Neuroscience showed that people can even learn completely new behaviors (in this case, to associate unpleasant and pleasant odors with certain sounds) while they are completely asleep.
• Plays a role in immune function.
  Your body produces special proteins called cytokines, which help your immune system fight off infection. According to the U.S. Department of Health and Human Services, more of these proteins are produced during sleep when you are sick, which is one of the reasons you may feel so tired when you have the flu. Rest gives the body the time it needs to produce these infection-fighting proteins and to restore itself to wellness.

How Much Sleep Do You Need?

You’ve probably heard that you should get a good amount of sleep each night. Not doing so will put you in what’s called “sleep debt,” and can lead to a host of symptoms and health issues.

Exactly how much sleep should you get? Sleep needs depend mostly on age, but they are also individual. Your sleep needs may also be affected by pregnancy, aging, sleep deprivation, and sleep quality.

If you get too little sleep you might consider making some lifestyle changes. But if that doesn’t work, you may want to speak with your doctor.

You may also want to tell your doctor if you’re getting too much sleep. It is possible to get too much of a good thing. Excessive sleepiness can be a sign of several different medical issues. And getting too much sleep can even lead to health risks.

Here are the current guidelines from the National Sleep Foundation:

Age	Hours of sleep per day
newborn baby	14 – 17 hours (includes naps)
infants	12 – 15 hours (includes naps)
toddlers	11 – 14 hours (includes naps)
preschool-age children	10 – 13 hours
school-age children	9 – 11 hours
teenagers	8 – 10 hours
adults	7 – 9 hours
seniors	7 – 8 hours

.

Tips for better sleep

1. Try a sleep schedule
Go to sleep and wake up at the same time every day, even on the weekends. When you go to bed and wake up at the same time each day, you condition your body to expect sleep during that time. You may eventually get into a rhythm where sleep comes more easily.

2. Create an ideal sleep environment
Being comfortable will help your body give in to sleep. Make sure your bedroom is cool, dark, and quiet. You may want to darken the room using curtains. Earplugs or a white-noise machine can help drown out distractions.

3. Power down your devices
Computer and phone screens emit what is called blue light. At night this kind of light can disrupt your body’s natural circadian rhythm and disrupt sleep. Power down your devices and limit your exposure to blue light in the two to three hours before bed.

4. Mind your lifestyle habits
Taking care of yourself during waking hours will help your sleep. Think about the things you consume. Caffeine may wind you up if consumed too close to bedtime. Alcohol can make you sleepy, but it actually makes your quality of sleep worse. Herbal tea or warm milk are better substitutes. Exercise is good for your body, but doing it right before you go to bed may disrupt your sleep.

5. Keep a sleep diary
If you have concerns about your sleep, write about them. Include anything and everything about your usual habits and routine so you can show your doctor. Be sure to jot down how long you sleep each night, how long it takes to fall asleep, if you nap during the day, and anything else related to your rest you think may be important.

 

A night without dreams is like a cupcake without frosting.” – Aeric