Rem Vs Nrem Sleep: What's The Difference?

Sleep is a complex and mysterious process that humans spend about a third of their lives doing. Understanding the differences between REM and NREM sleep is crucial to comprehending sleep as a whole.

REM (rapid-eye movement) sleep is characterised by increased brain activity and dreaming. The name comes from the way the eyes move rapidly behind closed eyelids. During REM sleep, the body experiences atonia, a temporary paralysis of the muscles, except for the eyes and the muscles that control breathing. This stage usually begins about 90 minutes after falling asleep and is associated with memory consolidation and the processing of emotions and emotional memories.

On the other hand, NREM (non-rapid eye movement) sleep consists of three stages of progressively deeper sleep. During the first stage, the body and brain activities start to slow down, with periods of brief movements. In the second stage, the body temperature drops, eye movements stop, and breathing and heart rate become more regular. The third stage is the deepest and is associated with tissue repair, muscle repair, immune system support, and the release of growth hormones.

REM sleep is associated with dreaming and is not considered restful, while NREM sleep is quiet sleep

Sleep is a complex and mysterious body process that humans spend about one-third of their lives doing. It is vital for the body and brain to rest, conserve energy, repair injuries, and recover. The body cycles between being awake and asleep, and during sleep, it goes through various stages of non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep.

NREM sleep is quiet sleep, consisting of four stages, each with unique characteristics, including variations in brain wave patterns, eye movements, and muscle tone. The first stage is the lightest stage of sleep, lasting only a few minutes, and is easy to wake someone up during this stage. The second stage is still light sleep but deeper than the first, with slower brain waves and no eye movements. This is when the body temperature drops and breathing and heart rate become more regular. The third and fourth stages are deep sleep, and it is harder to wake someone up during these stages. The body repairs and restores itself during deep sleep, and the immune system is strengthened.

On the other hand, REM sleep is active sleep, characterised by rapid eye movements, increased brain activity, and temporary paralysis of the body. It is associated with dreaming and emotional processing and is believed to be essential for memory consolidation and learning. While REM sleep is not considered restful, it is necessary for cognitive functions and emotional well-being.

A typical night's sleep consists of four to six sleep cycles, each lasting about 90 to 120 minutes. The sleep cycles progress as follows: NREM stage 1, NREM stage 2, NREM stage 3, repeat of NREM stage 2, and finally, REM sleep. The time spent in each stage changes throughout the night as the cycle repeats, and factors such as age, recent sleep patterns, and alcohol consumption can influence the sleep stages.

While NREM sleep is quiet and restorative, REM sleep is active and associated with dreaming and emotional processing. Both types of sleep are essential for the body and brain to function optimally.

NREM sleep is further divided into three stages, each with unique characteristics

During N1, the first stage of sleep, heartbeat, eye movements, brain waves, and breathing activity begin to slow down. Motor movements also decrease, although muscle twitches called hypnic jerks may occur. N1 usually only lasts a few minutes.

In N2, the second stage of sleep, the body experiences a further reduction in heart rate, breathing, muscle activity, and eye movements. Body temperature also drops. The brain begins to produce bursts of rapid, rhythmic brain wave activity, known as sleep spindles, which are thought to be a feature of memory consolidation. Sleep spindles have a frequency of approximately 7 to 15 Hertz and can be classified into two categories: slow or fast. N2 accounts for about 45% of total sleep time.

N3 is the deepest stage of NREM sleep and is also known as slow-wave sleep. During this stage, the heartbeat, breathing, muscle activity, and brain waves are at their slowest. The body releases growth hormones and carries out tissue, muscle, and bone repair. The majority of brain waves during N3 are called delta waves, which are large waves with a relatively slow frequency of 1 to 4 Hertz. N3 is the most difficult stage to wake someone from, and if they do wake up, they will likely experience sleep inertia, a state of confusion or "mental fog" that can last about 30 minutes.

The body cycles through all stages approximately 4 to 6 times each night, with each cycle lasting about 90 minutes

The human body cycles through all stages of sleep approximately 4 to 6 times each night, with each cycle lasting about 90 minutes. The first sleep cycle is often the shortest, ranging from 70 to 100 minutes, while later cycles tend to fall between 90 and 120 minutes. The first stage of the sleep cycle is a transition period between wakefulness and sleep. This stage usually lasts for around five to ten minutes. People spend about half of their total sleep time during the second stage of the sleep cycle, which lasts for about 20 minutes per cycle. The third stage is the deepest sleep stage and is harder to wake someone up from. This stage is when the body starts its physical repairs. The fourth and final stage is REM sleep, which is when most dreams occur. This stage usually starts 90 minutes after falling asleep.

Sleep quality and time spent in each sleep stage may be altered by depression, aging, traumatic brain injuries, medications, and circadian rhythm disorders

Sleep is a complex process that involves many parts of the brain. As such, any changes to the brain, whether from depression, aging, traumatic brain injuries, medications, or circadian rhythm disorders, can alter sleep quality and the time spent in each sleep stage.

Depression

Depression and sleep problems are closely intertwined. People with insomnia have a tenfold higher risk of developing depression, and among those with depression, 75% have trouble falling or staying asleep. Depression is associated with shortening the amount of restorative slow-wave sleep, which can weaken emotional resilience and make individuals more vulnerable to depression in the future.

Aging

As people age, their circadian rhythms change, often leading to disrupted sleep patterns. The body's internal clock, located in the suprachiasmatic nucleus (SCN) of the hypothalamus, deteriorates with age, disrupting circadian rhythms and affecting when people feel tired and alert. Older adults experience a phase advance, going to bed and waking up earlier. They spend more time in the earlier, lighter sleep stages and less time in the deeper stages, resulting in more fragmented sleep. Additionally, hormonal changes, such as decreased melatonin production, can further disrupt sleep in older adults.

Traumatic Brain Injuries

Traumatic brain injuries (TBIs) can cause various sleep disturbances, including insomnia, excessive daytime sleepiness, delayed sleep phase syndrome, narcolepsy, and sleep disorders like restless leg syndrome, bruxism, sleep apnea, and periodic limb movement disorder. The injury can affect the brain's ability to control sleep and wakefulness, alter breathing control during sleep, and change the way chemicals in the body affect sleep. Medications taken after a TBI can also impact sleep, with some causing insomnia or daytime sleepiness.

Medications

Medications can significantly impact sleep quality and time spent in each sleep stage. For example, prescription drugs for asthma and depression may cause insomnia, while stimulants taken too close to bedtime can have the same effect. Additionally, many over-the-counter sleep aids contain antihistamines, which are not recommended for people with TBI as they can cause memory disturbances and other side effects.

Circadian Rhythm Disorders

Circadian rhythm disorders disrupt the body's natural sleep-wake cycle, affecting sleep quality and timing. These disorders can be caused by various factors, including brain damage, vision impairments, travel across time zones, and shift work. Treatment for circadian rhythm disorders may involve adjusting lighting, taking supplemental melatonin, and making sleep behavior adjustments, such as maintaining a consistent sleep schedule and avoiding bright lights and electronic screens before bedtime.

NREM sleep is when the body starts its physical repairs, while REM sleep is when the brain processes emotions and emotional memories

Sleep is divided into two main types: non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. NREM sleep is further divided into four stages, each characterised by unique brain activity and physiology.

NREM sleep is when the body starts its physical repairs. The first stage of NREM sleep is a transitional period between wakefulness and sleep. During this stage, the body and brain start to slow down, with the heart rate, eye movements and breathing all decreasing. This stage lasts for around five to ten minutes.

The second stage of NREM sleep is when the body temperature drops, eye movements stop, and breathing and heart rate become more regular. This stage lasts for around 20 minutes per cycle and makes up about half of total sleep time.

The third stage of NREM sleep is when the body enters its deepest sleep. Muscle tone, pulse and breathing rate all decrease further, and the brain exhibits high-voltage, slow-wave activity. This is the stage when the body starts its physical repairs, with the release of growth hormones, tissue, muscle and bone repair, and immune system support.

REM sleep, meanwhile, is when the brain processes emotions and emotional memories. It is characterised by high levels of brain activity and dreaming. The eyes move rapidly beneath closed eyelids, and the body experiences temporary paralysis. This is believed to be nature's way of preventing people from acting out their dreams.

The sleep cycle progresses as follows: sleep begins with NREM stage 1, which progresses into NREM stage 2, followed by NREM stage 3, then back to NREM stage 2, and finally REM sleep. A complete sleep cycle takes around 90 to 120 minutes, and people typically go through four to six sleep cycles per night.

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