REM sleep is the stage during which rapid eye movements occur and dreams are most vivid. This stage is distinguished by high brain activity similar to wakefulness.

NREM Stage 3, also known as slow-wave sleep, is the deepest stage characterized by delta waves. It plays a critical role in physical restoration and memory consolidation.

NREM Stage 1 is the lightest stage that follows wakefulness, marking the transition into sleep. It is a brief stage before progressing into deeper sleep stages.

REM stands for Rapid Eye Movement, which describes the characteristic eye movements during this sleep stage. This stage is crucial for dreaming and aspects of memory consolidation.

Delta waves are mainly observed during deep sleep, particularly in NREM Stage 3. These slow waves indicate a high level of neuronal synchronization and restorative processes.

Most adults experience approximately 4 to 6 complete sleep cycles per night. Each cycle lasts about 90 minutes and includes alternating periods of NREM and REM sleep.

REM sleep is heavily involved in the consolidation of procedural memory, such as the learning of motor skills. Studies show that the brain's activity during REM helps integrate these memories.

The suprachiasmatic nucleus (SCN) is located in the hypothalamus and serves as the master clock of the body. It synchronizes the sleep-wake cycle with environmental light cues.

NREM Stage 2 sleep is defined by the presence of sleep spindles and K-complexes on the EEG. These patterns help maintain sleep continuity and assist in memory consolidation.

Melatonin, produced by the pineal gland, plays a critical role in signaling the body to prepare for sleep. Its production is influenced by the light-dark cycle, aligning with the circadian rhythm.

Acetylcholine levels are significantly elevated during REM sleep, which supports the brain's active and desynchronized state. This neurotransmitter is critical for triggering the vivid dreaming associated with REM.

Sleep spindles are believed to play a dual role in consolidating memory and protecting sleep by reducing the impact of external stimuli. Their occurrence is a hallmark of stage 2 sleep.

NREM Stage 3, also known as deep sleep, is essential for physical recovery and for triggering the release of growth hormones. This stage supports tissue repair and overall restorative processes.

Exposure to artificial light at night can interfere with melatonin production, thereby disrupting the circadian rhythm. This disruption often leads to altered sleep stages and diminished sleep quality.

A typical sleep cycle starts with NREM Stage 1, moves through Stage 2 and deep NREM Stage 3, then returns to Stage 2 before transitioning to REM sleep. This cycle is repeated several times throughout the night.

Sleep deprivation leads to reduced metabolic activity in the prefrontal cortex, impairing executive functions such as decision-making and attention. This area of the brain is especially vulnerable to the effects of insufficient sleep.

The suprachiasmatic nucleus (SCN) acts as the master clock in the brain, aligning physiological processes with the external light-dark cycle. It ensures that sleep and wakefulness occur at appropriate times based on environmental cues.

REM sleep behavior disorder is characterized by the absence of normal muscle paralysis during REM sleep, leading individuals to physically act out their dreams. This disorder has been linked to a higher risk of developing neurodegenerative conditions, such as Parkinson's disease.

Polysomnography relies on EEG, EOG, and EMG to provide a comprehensive view of sleep stages. These measurements record brain activity, eye movements, and muscle tone, which are crucial for accurate sleep stage classification.

Chronic disruptions in sleep stages can lead to imbalances in neurotransmitter systems that are essential for mood regulation. This dysregulation has been linked to a higher risk of developing mood disorders such as depression and anxiety.