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Stages of Sleep


Psychology & Sociology

Brainwaves are electrical activity from neurons and can be visualized with EEG. There are several types of brainwaves, including beta, alpha, theta, and delta waves. Beta waves are seen in a highly alert or concentrating state, while alpha waves occur during relaxation or daydreaming. Theta waves are present during sleep, and delta waves occur during deep sleep or a coma.

Sleep can be divided into stages: Stage 1 (known as NREM 1 or non-REM 1), Stage 2 (non-REM 2), and Stage 3 (non-REM 3 or slow wave sleep). Each stage is characterized by different brainwave patterns, with theta waves being dominant in Stages 1 and 2 and delta waves in Stage 3. During paradoxical sleep (a.k.a. rapid-eye movement or REM), brain activity mimics wakefulness (e.g. dreaming), but the body is paralyzed. It's also characterized characterized by alpha, beta, and desynchronous waves that lack clear pattern. A sleep cycle consists of progressing through every stage of sleep, typically taking around 90 minutes for an average adult, with most individuals completing 4 to 6 cycles in one night.

Lesson Outline

<ul> <li>Introduction to brainwaves</li> <ul> <li>Brainwaves are electrical activity in the cerebral cortex</li> <li>Measured using electroencephalography (EEG)</li> <li>Amplitude (voltage) describes the electrical intensity of brainwaves</li> <li>Frequency (Hertz) describes the speed of brainwaves</li> </ul> <li>Types of brainwaves</li> <ul> <li>Beta waves: high frequency (12.5 to 30 Hz), associated with high alertness and concentration</li> <li>Alpha waves: mid frequency (7.5 to 12.5 Hz), associated with relaxation and daydreaming</li> <li>Theta waves: low frequency (4 to 7 Hz), most common during sleep</li> <li>Delta waves: lowest frequency (0.5 to 4 Hz), associated with deep sleep and coma</li> </ul> <li>Stages of sleep</li> <ul> <li>Stage 1 - NREM 1</li> <ul> <li>Theta waves dominate brain activity</li> <li>Lightest stage of sleep</li> <li>Phenomena: hypnagogic hallucinations, hypnic jerks, and the Tetris effect</li> </ul> <li>Stage 2 - NREM 2</li> <ul> <li>Theta waves dominate brain activity</li> <li>Unique wave patterns: sleep spindles and K-complexes</li> </ul> <li>Stage 3 - NREM 3 or slow wave sleep</li> <ul> <li>Delta waves dominate brain activity</li> <li>Deepest stage of sleep</li> <li>Associated with sleepwalking and sleep talking</li> </ul> <li>Rapid-eye movement (REM) or paradoxical sleep</li> <ul> <li>Mix of alpha, beta, and desynchronous waves</li> <li>Similar brain activity to wakefulness, but body is paralyzed</li> <li>Most dreaming occurs during this stage</li> </ul> </ul> <li>Sleep cycles</li> <ul> <li>Progressions through every sleep stage</li> <li>Variable sleep cycle lengths for adults and children</li> <li>REM rebound effect when REM sleep is deprived</li> <li>Multiple sleep cycles occur each night</li> </ul> </ul>

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What are the different brainwaves associated with the various stages of sleep, and how are they measured?

Electroencephalography (EEG) is the primary tool used to measure brainwaves during sleep. The main brainwaves observed during sleep are theta and delta waves and patterns called sleep spindles and K-complexes. Theta waves are dominant in the initial stages of non-REM sleep, while delta waves are associated with deep, slow wave sleep. Sleep spindles and K-complexes are characteristic of Stage 2 of non-REM sleep and may help maintain the sleep state and protect against awakening.

What are the key features of REM sleep, and how does it differ from non-REM sleep?

Rapid eye movement (REM) sleep is characterized by rapid, random eye movements, increased brain activity, and vivid dreaming. It also includes temporary muscle paralysis, which prevents the dreamer from physically acting out their dreams. Non-REM sleep consists of three stages, transitioning from light to deep sleep. The key difference between REM and non-REM sleep is the presence of intense brain activity and eye movements in REM sleep, while non-REM sleep is associated with more restorative, slow brainwaves.

How do sleep cycles progress through the different stages of sleep throughout the night?

A typical sleep cycle lasts about 90 minutes. The sleep cycle typically begins with light non-REM sleep (Stage 1), and then progresses to deeper non-REM sleep (Stages 2 and 3). Stage 3, known as slow wave sleep, is the deepest stage of non-REM sleep. After Stage 3, the cycle may move back through Stage 2 before entering REM. Throughout the night, the duration of REM sleep increases while the duration of deep sleep (slow wave sleep) decreases.

What are the significance of sleep spindles and K-complexes during non-REM sleep?

Sleep spindles and K-complexes are unique electroencephalographic patterns observed during non-REM sleep, particularly Stage 2. Sleep spindles consist of brief bursts of high-frequency brain activity, while K-complexes are sharp, high-amplitude waveforms. Both sleep spindles and K-complexes are thought to play a role in sleep stabilization, memory consolidation, and protection against awakening from external stimuli. Additionally, they are involved in synaptic plasticity and brain development.

Why is slow wave sleep considered the most restorative stage of sleep?

Slow wave sleep, or deep non-REM sleep (Stage 3), is considered the most restorative stage of sleep because it is the period when the body undergoes various essential physiological processes. During slow wave sleep, the body releases growth hormone, repairs tissues, and strengthens the immune system. It's also a time when brain glucose metabolism and the clearance of toxic metabolites and proteins occur. Furthermore, slow wave sleep plays a crucial role in memory consolidation and cognitive function, helping the brain to recover from daily activities and prepare for the following day.