Which stage of sleep is characterized by sleep spindles and K-complexes?

Which stage of sleep is characterized by sleep spindles and K-complexes?

• A. Stage N1—transition to sleep with theta waves.
• B. REM—rapid eye movements and dreaming.
• C. Stage N3—slow-wave delta sleep.
• D. Stage N2—sleep spindles and K-complexes.

Answer: (D)

Sleep stage N2 is marked by sleep spindles and K-complexes. Sleep spindles are brief bursts of fast activity (about 12–16 Hz) that last a fraction of a second to a couple of seconds, while K-complexes are large, solitary waves followed by a smaller component. These features act as markers of a light but ongoing sleep state, helping to protect sleep by dampening brain responses to external stimuli and by facilitating the transition into deeper sleep later in the night. In contrast, REM sleep shows rapid eye movements and a more wake-like, low-amplitude, mixed-frequency EEG with dreaming, and stage N3 is dominated by slow, high-amplitude delta waves indicating deep, slow-wave sleep. The presence of spindles and K-complexes specifically identifies stage N2, distinguishing it from the other stages.

Sleep stage N2 is marked by sleep spindles and K-complexes. Sleep spindles are brief bursts of fast activity (about 12–16 Hz) that last a fraction of a second to a couple of seconds, while K-complexes are large, solitary waves followed by a smaller component. These features act as markers of a light but ongoing sleep state, helping to protect sleep by dampening brain responses to external stimuli and by facilitating the transition into deeper sleep later in the night.

In contrast, REM sleep shows rapid eye movements and a more wake-like, low-amplitude, mixed-frequency EEG with dreaming, and stage N3 is dominated by slow, high-amplitude delta waves indicating deep, slow-wave sleep. The presence of spindles and K-complexes specifically identifies stage N2, distinguishing it from the other stages.