Answer to Question 1
d
Answer to Question 2
As you begin sleeping, you are in Stage 1 sleep. Brain waves, as measured by EEG, are small and irregular with variable frequencies. This lasts only 2 minutes or so. Upon entering Stage 2 sleep, there are occasional bursts of brain activity in the EEG called sleep spindles. Approximately 50 of sleep is in Stage 2 . In Stages 3 and 4, large, slow delta waves begin to appear. In Stage 3, 50 or less of brain waves are delta; when the percentage increases past 50, you have moved into Stage 4 . Stages 3 and 4 are sometimes referred to as slow-wave sleep. These 4 stages are collectively known as NREM sleep. You then move back through the stages in reverse order.
After Stage 2 is reached, you move into Rapid Eye Movement (REM), or paradoxical, sleep. Here, your brain is active and you are likely to be dreaming. This process takes about 90 minutes, and you cycle through the stages four or five times in a typical
night.
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