Circadian rhythm is controlled by
(A) Suprechiasmatic nuclei # CIRCADIAN RHYTHMS:> Most if not all living cells plants and animals have rhythmic fluctuations in their function that are about 24 hours in length - i.e., they are circadian.> Most of the cells in the body have circadian rythms.> In liver these are all other cells the rhythms are entrained by the paired suprachiasmatic nuclei (SCN), one on either side, above the optic chiasm.> Have rhythmic fluctuations in their function that are about 24 hours in length--ie, they are circadian (L circa "about" + dia "day").> Normally they become entrained, ie, synchronized to the day-night light cycle in the environment.> If they are not entrained, they become progressively more out of phase with light-dark cycle because they are longer or shorter than 24 hours.> These nuclei receive information about the light-dark cycle via a special neural pathway, retinohypothalamic fibers that pass from the optic chiasm to the SCN.> Efferents from the SCN initiate neural & humoral signals that entrain a wide variety of well-known circadian rhythms. These include the rhythms in the secretion of ACTH and other pituitary hormones, the sleep-wake cycle, activity patterns, and the secretion of the pineal hormone melatonin.> Neurons in the SCN discharge rhythmically when removed from the body and cultured in vitro.> Genes in these neurons are activated diurnally, and their protein products enter the cytoplasm, where they modify cell function and thus neuronal discharge.
Suprechiasmatic nuclei
Raphe nuclei
Thlamus
Red nucleus
Misc.