Types Of Sleep

Introduction

Sleep is a regenerative process that affects every structure of our brain and body. A night of good and deep sleep is as important for the proper functioning of all bodily systems as food and water. Without it, it would be very difficult for us to remain concentrated on a task or remember information.

 

What Are the Types of Sleep?

According to the neuronal activity in the brain, we can distinguish 2 basic types of sleep:

  • Rapid-eye movement (REM)
  • Non-rapid eye movement (NREM)

 

While sleeping, we cycle through multiple phases of both REM and NREM sleep several times during the night. As the night progresses to the morning hours, the occurring REM phase tends to get longer. 

 

Rapid-Eye Movement (REM)

 

Rapid-eye movement denotes the short and quick movements of the eye in different directions. The REM phase occurs 90 minutes after the person falls asleep. The first REM phase of sleep lasts about 10 minutes. During this phase, the eyes rapidly move behind the closed eyelids, hence the name of this phase.

 

Even though some of our dreams occur in the non-rapid eye movement (NREM) phase, most of them take place in the rapid-eye movement (REM) phase.

 

Non-Rapid Eye Movement (NREM) 

 

We can distinguish 3 different phases of non-rapid eye movement (NREM):

 

  • Phase 1 (NREM wakefulness to sleep) – In the first phase of sleep, we can easily wake up even though our eyes are firmly closed. This non-rapid eye movement phase (NREM) is a transition from the wake phase to sleep. While this period lasts ( 5-10 minutes), our muscles relax and our breathing, heartbeat, and the movements of our eyes slow down. Also, the functions that were active during the wake phase start to slow down. 
  • Phase 2 (NREM light sleep) – This phase is characterized by light sleep that occurs before the phase of deep sleep. All the functions of the body relax even more and the body temperature is lowered. In this way, the body is ready for deep sleep.  
  • Phase 3 (NREM deep sleep) – Deep sleep occurs in phase 3 of NREM. The heartbeat and breathing are at their lowest level. Waking up is not as easy in deep sleep as in the previous phases. Even the brain waves are at their slowest rate in this phase. 

 

Even though our bodily functions are at their slowest, the fact is that the brain itself never sleeps. When a person wakes up from the deep sleep, waking up is usually accompanied by a few moments of disorientation which lasts until all systems and processes of the body are fully awakened and functioning again. 

 

What Are the Sleep Mechanisms?

 

There are 2 internal biological mechanisms involved in the regulation of our sleep/wake cycles:

  • Circadian rhythms
  • Sleep-wake homeostasis

 

Circadian Rhythms

 

The circadian rhythms support and determine the sleeping pattern of every individual. Being linked to the internal clock of the body and the sleep/wake cycle, these rhythms determine the time our body and brain need to rest, how long will the rest last, and at what time they should receive their nutrition.

 

Sleep-Wake Homeostasis

 

The sleep-wake homeostasis is a term that denotes the need for sleep of every individual. This drive triggers the need for the rest of the body and brain and also determines the intensity of sleep. 

 

This homeostasis is determined by the health of the individual, the nutrition, the surroundings where the individual sleeps, as well as stress and medications. 

 

Why Is Sleep Important?

Sleep has several important functions:

 

  • Restoration – Sleep serves as a means for the physical restoration of our body. During the sleeping phases, the body heals by removing the metabolic waste and toxins accumulated in the phase of wakefulness. This is why a lack of sleep can exacerbate medical conditions.
  • Memory processing – Sleep is beneficial for the storage of our memories and learned information. While the sensory information and data we’ve received are encoded during the phase of wakefulness, those memories are consolidated and more easily stored in both short-term and long-term memory during the phases of sleep.
  • Dreaming – Dreaming occurs in all stages of sleep. However, dreams are most vivid during the rapid-eye movement stage. These elusive experiences occur as a result of the electrical impulses shared between the cerebral cortex neurons during the REM phase. Dreams support the storing of memories and also aid in sorting our feelings and thoughts.

 

How Many Hours of Sleep Do We Need?

 

The number of hours we spend sleeping is generally determined by the age of the individual, although there are many other factors, such as health conditions, activities, and obligations that influence the amount of sleep we get.

 

In general, newborn babies and infants need approximately 14 to 18 hours of sleep per day to grow and develop. On average, toddlers require about 11 to 14 hours of sleep a day, while pre-school children and teenagers are more active during the day and they need about 9 to 10 hours of a good night’s sleep.

 

The average sleeping hours for adults amount from 7 to 9 hours of sleep at night, whereas adults over 65 years of age require less time to sleep due to the effects of medications they take and lowered physical activity.

 

What Are the Types of Sleep Disorders?

 

A night of poor quality sleep or a chronic lack of sleep can lead to numerous impairments of brain and bodily functions. Longer periods spent without a deep, regenerative sleep can trigger elevated levels of blood pressure, obesity, or depression.

 

In the long term, lack of sleep can also result in:

 

  • Insomnia;
  • Sleep apnea;
  • Narcolepsy;
  • Restless leg syndrome;
  • Parasomnias;
  • And sleep-walking.

 

Insomnia 

Insomnia is a sleep disorder that can occur incidentally, be short-termed, or last for a prolonged time (become a chronic disorder). Very often, the main causes of insomnia are excessive worrying about school or work situations, emotional or family problems, stress, trauma, etc. 

 

There are several types of insomnia:

 

  • Acute insomnia – This type refers to short-term insomnia, usually triggered by a stressful or traumatic event. It’s a brief episode when the affected individual has difficulty falling asleep. Acute insomnia lasts until the stressful event is resolved. 
  • Chronic insomnia – When the pattern marked with lack of sleep repeats more than 3 times a week and lasts for several months, it’s defined as chronic insomnia. This type of insomnia also relates to stressful events, but it can be exacerbated by some other factors such as mental health disorders, underlying health problems, poor sleep hygiene, continuous change of the sleep/wake pattern, certain medications, etc.
  • Comorbid insomnia – If insomnia is the result of an underlying medical condition, it’s referred to as comorbid insomnia. The sleeping problem is most often triggered by sleep apnea, depression, anxiety, gastroesophageal reflux, etc. 
  • Sleep-onset insomnia – In cases when a person has difficulty falling asleep at night, we distinguish sleep-onset insomnia. Most of the affected individuals are unable to fall asleep for more than 30 minutes after they go to bed. Tossing and turning in bed while struggling to fall asleep is a common depiction of this type of insomnia.
  • Sleep maintenance insomnia – Waking up in the middle of the night and struggling to fall asleep again is the main characteristic of the sleep maintenance insomnia. Namely, the person affected by this type of insomnia faces difficulty in maintaining uninterrupted sleep throughout the night.

 

Sleep Apnea

 

Sleep apnea is a potentially life-endangering sleep disorder that’s characterized by obstruction of breathing during sleep. Snoring and fatigue in the wake phase are the main symptoms of this type of sleep disorder.

 

There are 3 main classifications of sleep apnea:

  • Obstructive sleep apnea – Sleep apnea occurs when the muscles supporting the tongue and the palette relax temporarily. The relaxed muscles narrow the airways, which obstructs breathing. 
  • Central sleep apnea – When breathing continuously stops and resumes during sleep, we refer to it as central sleep apnea. This occurs due to the failure of the brain to send the right signals to the muscles that are in charge of controlling and regulating breathing. 
  • Complex sleep apnea syndrome – This type of apnea incorporates all of the aforementioned symptoms. It’s triggered by some medical conditions, such as heart failure or stroke. Also, sleeping at high altitudes, where oxygen concentration is different from that of the normal sleeping environment, may lead to the occurrence of complex sleep apnea syndrome. 

What Are the Symptoms of Sleep Apnea?

The typical symptoms of sleep apnea include:

  • Waking up with a headache;
  • All types of insomnia;
  • Inability to concentrate on a task, conversation, or activity;
  • Irritability;
  • Dryness of mouth;
  • Episodes of obstructed breathing during the sleep;
  • Struggling for air during sleep.

 

Narcolepsy

Excessive sleepiness, hallucinations, and sleep paralysis are the typical symptoms of narcolepsy. It’s a sleep disorder that makes affected individuals feel extremely sleepy during the day. They may even fall asleep anywhere against their will. 

 

Narcolepsy triggers hallucinations and blurs the reality during the wake phase. People who suffer from this sleep disorder frequently experience nightmares and are unable to maintain a continuous night’s sleep.

 

Restless Leg Syndrome 

 

Also known as the Willis-Ekbom Syndrome, this neurologic sensorimotor sleep disorder is characterized by involuntary urges to move the legs during sleep. Applied pressure or voluntary movement of the restless leg can relieve the symptoms which disrupt the sleep of the affected individual.

 

Parasomnias

 

Parasomnias include abnormal behaviors during the phases of sleep. They include:

 

  • Talking in sleep – This sleep disorder is the least harmful of all parasomnias. On the other hand, it might signify the existence of a more serious underlying health condition.  Prolonged periods of lack of sleep, alcohol abuse, stress, depression, and anxiety, can lead to talking in sleep. 
  • Night terrors – Individuals who suffer from night terrors tend to wake up frightened in the middle of a dream without being able to point out what had them terrified. This sleep disorder is most common among children.  
  • Sleep-related late-night eating disorder – When the affected individuals (usually sleepwalkers) involuntary reach for food in a sleepy state, they risk eating something that’s bad for their health or is not even food. 
  • Teeth grinding – This sleep disorder is also labeled as bruxism. The involuntary grinding of teeth can lead to even more serious health consequences, such as damaged teeth, migraines, pain in the jaw, etc. Bruxism can occur due to anxiety, stress, alcohol intake, sleep apnea, caffeine consumption, etc. 
  • Nightmares – Bad dreams occur due to the neuronal activity in the amygdala, the cortical structure involved in the processing of feelings of fear and anxiety. The activity that occurs in order to detect potential threats produces nightmares during the rapid-eye movement phase. Stress and anxiety are the major triggers of nightmares. 

 

Sleep-Walking

 

Sleep-walking or somnambulism refers to a behavior disorder that occurs during the non-rapid eye (NREM) movement phase of deep sleep. Children are more often affected by this disorder than adults. 

 

How Do Electronics Influence Our Sleep?

The photoreceptors located in the retina of our eyes support the wakeful phase by translating sensory stimuli into information, synchronized with the circadian rhythms of the body. When the brain receives a signal from the environment that it’s daytime, it promotes the wake phase. On the other hand, when it receives information that it’s dark outside, the brain triggers the sleep phases. 

 

This is why electronics in our bedroom prevent our good night’s sleep. As such, by emitting light, our TVs, computers, tablets, or smartphones send misinformation to our brain about our environment, confusing night and day. Due to this, the brain signals the relevant cortical structures to suppress the production of melatonin – the hormone that triggers sleep. 

 

This promotes wakefulness instead of sleep which can be extremely harmful in the long-term. That is to say, lack of sleep during the night can lead to increased daytime sleepiness, lowered ability to concentrate, difficulty falling asleep at night, mood changes, irritability, eating disorders and obesity, etc. A book, for example, is the best item to replace the electronics in our bedroom while promoting a good night’s sleep.

 

Fun Facts

Did you know?

 

  1. We tend to wake up at 3 am because at this particular time we shift from a night of deep sleep into a lighter sleep.
  2. We spend around a third of our lifetime sleeping. 
  3. Consumption of caffeine, alcohol, and nicotine later at night can deprive us of sleep. 
  4. Setting a schedule for waking up and going to bed at the same time every day contributes to a good night’s sleep. 
  5. Individuals who work night shifts often have a disrupted sleep/wake cycle and circadian rhythm. 
  6. Flying to a different time zone creates confusion between the internal clock of the individual and the real-time clock, which also interrupts the circadian cycles of the body. 
  7. An adult individual usually needs from 7 to 9 hours of a good night’s sleep to maintain the sleep-wake homeostasis. 
  8. We usually spend 2 hours dreaming each night, but we rarely remember much of what we’ve dreamt about. 
  9. The REM phase is when the most vivid dreams occur during our sleep.
  10. Relaxing in a warm bath or shower, and treating yourself to a warm cup of tea or milk after it is a great ‘recipe’ for a good night’s sleep.