Figure 1.5-4 (Measuring Sleep)

Shows electrodes on scalp (EEG = brain waves), chin (EMG = muscle tension), and near eyes (EOG = eye movements). Other devices can measure heart rate, breathing, genital arousal.

Figure 1.5-5 (Brain Waves & Sleep Stages)

Beta waves = awake; Alpha waves = relaxed; Delta waves = deep Stage 3 (N3) sleep; REM waves = look like Stage 1 but body is internally aroused.

Figure 1.5-6 (Moment of Sleep)

Shows transition from awake to sleep (Stage 1/N1) is gradual; we are unaware of the exact moment we fall asleep.

Figure 1.5-7 (Typical Night’s Sleep)

Sleep cycle repeats ~90 minutes; Stage 3 shortens as night goes on; REM and Stage 2 get longer; cycles adjust with age (more awakenings in older adults).

AP Exam Tip Figure clarification

REM does not come directly after Stage 3; usually Stage 2 follows Stage 3, then REM.