What is the primary function of the Suprachiasmatic Nucleus (SCN)?

The Suprachiasmatic Nucleus (SCN) is a small region located in the hypothalamus that plays a crucial role in regulating circadian rhythms, which are the physical, mental, and behavioral changes that follow a daily cycle. These rhythms are influenced by environmental cues, especially light and darkness in light–dark cycles. The SCN receives information from the retina about the light-dark cycle and uses this information to synchronize the body's internal clock with the external environment.

This synchronization is essential for numerous biological processes including sleep-wake cycles, hormone release, and body temperature regulation. By setting the pace for these daily biological cycles, the SCN helps ensure that bodily functions occur at optimal times, leading to improved overall health and functioning. Therefore, its primary function is to establish and maintain these rhythms, making option B the correct answer.