Answer:
- Typically begins about 20 minutes after stage 1: Stage 3
- Alpha waves dominate: Stage 1
- Sleep spindles occur: Stage 2
- Light sleep: Stage 2
- Vital signs are at their lowest levels: Stage 4
- Delta waves dominate: Stage 4
- Feeling a drifting sensation: Stage 1
- Beginning of decline in respiration and blood pressure: Stage 2
Explanation:
Sleep can be divided into two phases: 1-non-rapid eye movement (NREM) sleep and 2-rapid eye movement (REM) sleep. In turn, NREM sleep is divided into four stages (1 to 4). Stages 1-2 are referred to as “light sleep”, while stages 3-4 are known as “deep sleep”. The first NREM stage (normal length: 5-10 minutes) is the transition between wakefulness and sleep. During this stage, the brain produces high amplitude theta waves. During the second NREM stage (light sleep, 10-25 minutes), the body temperature drops, muscles are in a more relaxed state, the breathing and heart rate also drop. The third NREM stage (20-40 minutes) involves the emergence of delta waves and muscles are entirely relaxed. This period (stage 3) is a period of deep sleep, which is referred to as slow-wave sleep (SWS). Finally, the fourth NREM stage (10-60 minutes) is characterized by high amplitude delta waves, while heart and respiration rates slow dramatically.
