The initial stage of NREM sleep is known as which stage?

• A. NREM stage 2
• B. NREM stage 1
• C. REM sleep
• D. NREM stage 3

Answer: (B)

NREM sleep begins with a brief, light transition from wakefulness into sleep. This initial phase is stage one of NREM. In this stage, brain activity slows to theta waves, you’re relatively easy to awaken, and you may experience brief muscle jerks or a sensation of falling as you drift off. It’s the lightest part of sleep and lasts only a few minutes before you typically progress into deeper NREM phases. After this, sleep moves into stage two with characteristic spindles and K-complexes, then into deeper slow-wave sleep, while REM sleep comes later with rapid eye movements and dreaming.