Fig. 2

The three main components of the central circadian system: 1) central clock in the SCN; 2) input pathways, and 3) output pathways. IpRGCs provide photic inputs and RAPHE provides non-photic inputs to the SCN. IGL, which receives inputs from both ipRGCs and RAPHE, also send signals to the SCN. The neurotransmitter in each pathway is shown: GLU for glutamate; GABA for gamma-Aminobutyric acid; 5HT (serotonin). RAPHE: the raphe nuclei; IGL: the intergeniculate leaflet