The first system is our nearly twenty-four-hour circadian cycle regulated by a specialized group of cells within a region of the brain known as the hypothalamus.52 (The sleep-inducing name for this cluster of cells is the suprachiasmatic nucleus.) These cells wake us up in the morning by signaling to the glands atop our kidneys to produce cortisol, the major hormone that stimulates the body to spend energy. Then as darkness falls, the hypothalamus directs the pineal gland, another structure in the brain, to produce melatonin, the “Dracula hormone,” which helps induce sleep.
