Fig. 1
From: Circadian rhythms in the blood–brain barrier: impact on neurological disorders and stress responses
General interactions between the central clock and peripheral clocks. The central clock, located in the SCN, creates an autonomous circadian rhythm; however, signals from the environment termed “zeitgebers” (German for “time giver”) also influence these rhythms. In the SCN, the most common of these zeitgebers is light from both artificial and natural sources. Peripheral clocks are synchronized vertically by the SCN through neural and humoral pathways, and horizontally by zeitgebers such as temperature and nutrition