Evie Summers
Sleep is divided into four stages and two phases: non-rapid eye movement (NREM) and rapid eye movement (REM). The first three stages are NREM sleep, while the fourth and final stage is REM sleep. The first stage of sleep, N1, is a transitional phase between wakefulness and sleep, during which the body and brain start to slow down. The second stage, N2, is a deeper sleep, where the body relaxes further and the heart rate and breathing slow down. The third and fourth stages, N3 and REM, are deep sleep. During REM sleep, the eyes move rapidly, brain waves are similar to those during wakefulness, and the body becomes temporarily paralysed as we dream. The sleep cycle then repeats itself, with each cycle lasting around 90 minutes.
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What You'll Learn
Dreaming occurs
During REM sleep, the body becomes temporarily paralysed, with the breath rate increasing. The first REM period is short, and as the night progresses, longer periods of REM sleep occur, along with decreased time in deep sleep (NREM). Sleepwalking and night terrors are unique characteristics of N3, the final stage of non-REM sleep. Sleepwalking occurs when sleeping and waking states are combined, resulting in the individual wandering around in a dazed and uncoordinated state. Night terrors are partial wakings from sleep, during which behaviours such as screaming, kicking, and panic occur.
The transition between sleep stages reflects different aspects of sleep and the corresponding brain activity. During the early portion of stage one sleep, the brain produces alpha waves, which are relatively low-frequency, high-amplitude patterns of electrical activity. As an individual progresses through stage one sleep, theta wave activity increases. Theta waves are even lower frequency and higher amplitude than alpha waves.
The first three stages of sleep are non-REM sleep, with each stage leading to progressively deeper sleep. The fourth and final stage is REM sleep. Approximately 75% of sleep is spent in the non-REM stages, with the majority spent in stage two, or light sleep.
REM sleep was once believed to be the most important sleep phase for learning and memory. However, newer data suggests that non-REM sleep is more important for these tasks and is the more restful and restorative phase.
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Brain activity increases
Sleep is composed of several different stages, each with distinct patterns of brain wave activity. Brain wave activity can be visualized using EEG and is distinguished by the frequency and amplitude of brain waves.
The final stage of sleep is REM sleep, which is marked by rapid eye movements and an almost complete paralysis of the body. Dreaming occurs during this stage, and the brain shows increased activity, resembling an alert state. Brain waves during REM sleep are similar to those observed during wakefulness, with higher frequencies and lower amplitudes.
During REM sleep, the brain is highly active and exhibits brain waves similar to those seen during wakefulness. This stage is crucial for learning, memory, emotional processing, and regulation. If individuals are deprived of REM sleep, they will experience a REM rebound, spending more time in this stage to compensate.
The transition from non-REM to REM sleep is characterized by a significant increase in brain activity. During non-REM sleep, brain activity slows down, with periods of brief movements. As individuals progress through the stages of non-REM sleep, brain activity gradually changes, with a decrease in alpha waves and an increase in theta wave activity.
Overall, the brain remains highly active during sleep, performing vital functions and ensuring our overall health and well-being.
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Body is temporarily paralysed
During the REM sleep stage, the body becomes temporarily paralysed. This is the fourth and final stage of sleep, and it is when most dreaming occurs. Brain activity increases during this stage, resembling the brain waves observed during wakefulness. However, the body is in a state of paralysis, with muscles completely relaxed and the body becoming inactive. This stage is also referred to as "slow-wave sleep" due to the presence of delta waves, indicating a deeper state of sleep compared to the previous stages.
The transition to REM sleep is marked by rapid eye movements, and it is when the eyes move rapidly behind closed eyelids. The body's breath rate increases during this stage, and the paralysis ensures that we remain unharmed as we dream. This stage of sleep is crucial for our overall health, and it is when the body performs various health-promoting functions. It is during REM sleep that the body recovers and grows, allowing for bodily recovery and certain types of learning.
The duration of REM sleep varies with each cycle, starting at around 10 minutes during the first cycle and increasing with each subsequent cycle. A typical night's sleep consists of 4 to 5 sleep cycles, and the progression of sleep stages follows a specific order: N1, N2, N3, N2, and finally, REM sleep. On average, a complete sleep cycle takes about 90 to 110 minutes.
During the REM stage, certain neurons in the brain are inhibited, resulting in the paralysis of the body. This temporary paralysis is a safety mechanism that prevents us from acting out our dreams and ensures we remain relaxed and inactive during sleep. The paralysis is so profound that it may be challenging to awaken someone from this stage of sleep.
The cycle then repeats, with each subsequent cycle spending less time in the deeper stages of sleep (N3) and more time in REM sleep. This progression reflects the changing nature of sleep throughout the night, with longer periods of REM sleep and decreased time in deep sleep as the night progresses.
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Eyes move rapidly
Sleep is divided into two phases: non-rapid eye movement (NREM) and rapid eye movement (REM). The first three stages of sleep are NREM sleep, while the fourth and final stage is REM sleep.
REM sleep is defined by rapid eye movements behind closed eyelids. Brain waves during this stage are similar to brain waves during wakefulness. The breath rate increases and the body becomes temporarily paralysed as we dream.
During REM sleep, the eyes dart rapidly behind closed eyelids. This is the stage where most dreaming occurs, and brain activity increases. The body becomes temporarily paralysed. Dreaming during REM sleep is often vivid, and the brain shows increased activity, resembling an alert state.
If someone is deprived of REM sleep and then allowed to sleep without disturbance, they will spend more time in REM sleep in what appears to be an attempt to compensate for the lost time. This is known as REM rebound, suggesting that REM sleep is regulated homeostatically.
The first three stages of NREM sleep lead to progressively deeper sleep. The first stage, N1, occurs when a person first falls asleep and usually lasts one to seven minutes. During this stage, the body hasn't fully relaxed, but body and brain activities start to slow, with periods of brief movements.
The final stage of NREM sleep, N3, is the deepest sleep stage. This stage is also referred to as slow-wave sleep due to the presence of delta waves, or slow brain waves.
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Breath rate increases
Sleep is a period during which the brain engages in activities necessary for life and closely linked to one's quality of life. A typical night of sleep consists of 4 to 5 sleep cycles, with each cycle lasting roughly 90 to 110 minutes. The first three stages of sleep are non-rapid eye movement (NREM) sleep, with each stage leading to progressively deeper sleep. The final stage of NREM sleep, N3, is the deepest stage of sleep, during which the body performs various health-promoting functions.
During the first stage of NREM sleep, the body hasn't fully relaxed, but body and brain activities start to slow, with a decrease in respiration and heart rate. As an individual progresses through the first stage of sleep, there is an increase in theta wave activity. Theta waves are low-frequency, high-amplitude brain waves that indicate a state of relaxation.
The second stage of NREM sleep is when the body goes into a state of deep relaxation, with a further decrease in heart rate and breathing. The third and fourth stages of NREM sleep are deep sleep, during which the body recovers and grows. During the third stage, the body reaches its lowest levels of muscle relaxation, heart rate, and breathing.
The fourth and final stage of sleep is REM sleep, which is characterised by rapid eye movements, increased brain activity, and temporary paralysis of the body. Dreaming also occurs during this stage. As the night progresses, longer periods are spent in REM sleep and less time is spent in deep sleep (NREM). During REM sleep, the breath rate increases as the body enters a state of dreaming. The cycle then repeats, with each cycle consisting of less deep sleep and more REM sleep.
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Frequently asked questions
Stage 5, or REM sleep, is characterised by rapid eye movements, an almost complete paralysis of the body, and a tendency to dream.
The first REM period is short, but as the night progresses, longer periods of REM occur. The final REM cycle may last 30 to 60 minutes.
During REM sleep, brain waves become faster and more similar to the waves observed during wakefulness. This is when vivid dreaming occurs, and the brain shows increased activity.
The sleep cycle is composed of 4 stages and 2 phases, all of which contribute to your overall health. The first 3 stages are non-REM sleep (N1-N3), and the final stage is REM sleep.
