Figure 1.

The orexin system helps integrate motivating signals into arousal responses. This schematic summarizes putative pathways through which signals related to sleep, stress, motivation, and hunger activate the orexin neurons to drive various aspects of arousal. Circadian timing signals that arise in the suprachiasmatic nucleus (SCN) are probably relayed through the dorsomedial nucleus of the hypothalamus (DMH). Many input signals are neurally mediated, but the orexin neurons may also respond to humoral signals associated with hunger such as ghrelin or low glucose.