The introduction reads as follows: The suprachiasmatic nucleus (SCN) of the hypothalamus is the body’s internal master clock, playing a role in regulating our circadian rhythms. These rhythms roughly follow the 24-hour cycle of daylight and darkness. But one doesn’t have to consciously perceive light for the SCN to function properly; there is a dedicated, nonvisual pathway that carries light information from the eyes to the SCN.The main graphic shows a man facing right, with an illustration of the brain overlaying the image. Four structures are identified at the center of the brain as follows:
At the center of the brain is an oval structure with a callout reading, “Hypothalamus regulates patterns of hunger and temperature.”
A cross-section is indicated by a flat plate through the brain at a point through the center of the eyes, with an arrow pointing to an illustration of that cross-section of the brain and eyes. The text reads as follows: The SCN is located deep in the brain, far away from visual processing areas. So how does it get information about light? Our eyes contain a separate nonvisual pathway made of retinal ganglion cells. This pathway goes directly to the SCN.In the cross-section illustration, colored lines lead from the eyes at front to structures in the brain. Lines lead from each eye to the SCN with a callout reading, “Nonvisual pathway for signals about light.” Lines lead from each eye, crossing at the front of the brain in an area labeled “Optic chiasm” and continuing into the brain tissue along paths labeled “Pathway for visual information” to ovals labeled “Visual processing area.” A callout reads, “Supra is Latin for “above.” Suprachiasmatic means “above the chiasm.” The SCN’s long name helps you find it in the brain!” At the bottom is an image of two men working in a control room containing banks of controls and dials. The text reads as follows: For the 20% of the U.S. workforce doing shift work, normal sleep schedules are disrupted. This leads to health problems and increased accidents (Harrington, 2001). Using what we know about how the SCN works, researchers are helping industries ease these effects. Bright lights, such as those installed in this power station control room, contain a high proportion of the blue light found in morning sun, fooling the SCN into thinking it is daytime. That makes it easier for workers to synchronize sleep patterns with work activities.