The pineal gland contains a circadian pacemaker in some vertebrates, such as perching birds (passerines).

In humans this function is taken over by the SCN in the anterior hypothalamus, which controls the…

Fibres leave the SCN to reach the ventrolateral preoptic area (VLPO) of the anterior hypothalamus multisynaptically. They initially relay in the sub-paraventricular zone before synapsing predominantly in the dorsomedial nucleus of…

The clock in the SCN, through its neurological connections, has a circadian influence not only on sleep, but also on temperature control, hormone secretion and other functions. The multisynaptic processing of the SCN…

Circadian rhythm periodicity
Circadian rhythms have a periodicity of around a day, which is longer than ultradian rhythms of,  for instance, REM sleep and shorter than infradian rhythms such as the menstrual cycle. The…

Impulses reach the SCN from retinal receptors which lie particularly in the lower and nasal quadrant of the retina. The receptors are the retinal ganglion cells and their light-sensitive pigment is…

The characteristics of this rhythm generator are largely genetically determined. At least 12 genes have been identified on chromosome 5 which, through inhibiting or promoting protein transcription, form a complex negative…