In stage 2 non-REM sleep, which feature is typical?

In stage 2 non-REM sleep, which feature is typical?

• A. Delta waves dominate
• B. Sleep spindles are present
• C. P waves are prominent
• D. REM features appear

Answer: (B)

Sleep spindles are the hallmark of stage 2 non-REM sleep. These are brief bursts of distinct 11–16 Hz activity lasting about a second or two, produced by thalamocortical circuits to help inhibit sensory input and keep you asleep. In stage 2 you also typically see K-complexes—large, single-wave spikes that often respond to stimuli—alongside background theta activity. This combination differentiates stage 2 from lighter sleep (where spindles and K-complexes aren’t present) and from deeper sleep, where delta waves become dominant. REM sleep, by contrast, brings rapid eye movements and characteristic sawtooth waves with little muscle tone, not stage 2. So, the presence of sleep spindles best fits stage 2 non-REM sleep.

Sleep spindles are the hallmark of stage 2 non-REM sleep. These are brief bursts of distinct 11–16 Hz activity lasting about a second or two, produced by thalamocortical circuits to help inhibit sensory input and keep you asleep. In stage 2 you also typically see K-complexes—large, single-wave spikes that often respond to stimuli—alongside background theta activity. This combination differentiates stage 2 from lighter sleep (where spindles and K-complexes aren’t present) and from deeper sleep, where delta waves become dominant. REM sleep, by contrast, brings rapid eye movements and characteristic sawtooth waves with little muscle tone, not stage 2. So, the presence of sleep spindles best fits stage 2 non-REM sleep.