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. Author manuscript; available in PMC: 2018 Feb 22.
Published in final edited form as: Neuron. 2017 Feb 22;93(4):747–765. doi: 10.1016/j.neuron.2017.01.014

Figure 7. Neural pathways that regulate the circadian timing of sleep and other rhythms.

Figure 7

The suprachiasmatic nucleus is the master circadian pacemaker and sits just above the optic chiasm. Neuronal rhythms generated by the SCN are synchronized with the daily light-dark cycle by direct inputs from the retina via the retinohypothalamic tract (RHT). The RHT also has small projections that may influence the activity of sleep-promoting neurons in the preoptic area. Most output signals of the SCN are relayed through the subparaventricular zone (SPZ) and then to the dorsomedial nucleus of the hypothalamus (DMH). The DMH regulates the timing of wakefulness via excitatory projections to the orexin neurons and locus coeruleus and inhibitory projections to the preoptic area. Signals from the SPZ and DMH also regulate the circadian rhythms of heart rate, blood pressure, body temperature, locomotor activity, and feeding. Circadian signals to the paraventricular nucleus of the hypothalamus regulate the daily melatonin rhythm.