Across the hours of each day, the arousal level of the brain rises and falls. Most of this variation is controlled by a tiny cluster of about 20,000 cells located in the hypothalamus (Mistlberger, 2005). These cells are responsible for controlling many rhythms in the body, including a rhythm of arousal increases and decreases spanning roughly a 24-hour period. This is why the sleep-wake rhythm is called circadian—from the Latin circa (“nearly”) and dies (“day”) (Figure 6.11).
· SLEEP AND WAKE CYCLES,
· THE NEED FOR SLEEP,
· THE FUNCTION OF SLEEP,
· WHY DO WEDREAM ?
· SLEEP, DREAMS , AND CONSCIOUSNESS