Suprachiasmatic nucleus:center of mammalian biological clock

Abstract
Revolutions of the earth around the sun and its polar axis give rise to the unfailing seasonal procession, and movements of the moon in relation to the earth and the sun give rise to the lunar month and to the tidal cycles. Given the occurrence of all these cycles, it is not surprising to find that most organisms show rhythmic modulations in their bodily processes and behaviour as predictive and adaptive mechanisms. Biological rhythms are the natural cycle of change in our body’s chemicals or functions. These rhythms display an endogenous, entrainable oscillation of a definite period and driven by a circadian clock, widely observed in plants, animals, fungi, and cyanobacteria. Anatomically circadian system consists of an oscillatory machine, including a central pacemaker, the Suprachiasmatic nucleus (SCN) in the hypothalamus, peripheral oscillators located in most tissues, various input tract and output tracts. The retina of the eye contains “classical” photoreceptors (rods and cones), which are used for conventional vision. But the retina also contains specialized ganglion cells which are directly photosensitive, and project directly to the SCN where they help in the entrainment of this master circadian clock. These cells contain the photopigment melanopsin and their signals follow a pathway called the retinohypothalamic tract, leading to the SCN. Non photic information can also be send by other tract like geniculohypothalamic tract. The SCN takes the information on the lengths of the day and night from the retina and other tract, interprets it, and passes it on to the other neural center and to the pineal gland, to synchronize the various body activities in rhythmic manner. Use of time as Chronotherapy can help to reduce adverse drug reactions and optimize drug efficacy by timing drug administration in accordance with the body’s circadian rhythms. Time management can increase the performance efficiency of animal by using management of time with different physiological and biochemical reactions of body. So, Timing is everything, and optimal circadian timing in animal bodily tissues is a key aspect of well-adapted physiology and behaviour.