BIOLOGICAL CLOCK

Human Biological Clock

A biological a clock is a self–sustained- internal timing mechanism that controls cyclic pattern, or rhytms, of a living organism. By providing temporal information , such as the time of day, month, or season, nearly all organism are adapted to event in both their internal or external environments. The product of this internal timing are physiological or behavioral even that, over time , vary in intensity.

Such biology time - dependent variability is expressed as a rhythm, or oscillation, with frequency equal to that of the underlying biological clock. Rhythms that occur more than once a day are called ultradian rhythm; one a day circadian; once a lunar day, lunar; and a once of year, circanual.

Ultradian Rhythm

In some cases the frequency of an oscillation may be high, or, conversely, the period of the oscillation may be brief. Certain rhythms of brain associated with sleep can occur with frequency of approximately seven cycle per second. Another ultradian rhythm is the release of luteinizing hormone from pituitary gland of male mammal. This chemical, wich helps maintain reproductive activity of the testes, is release from the pituitary of male in pulses approximately 1-2 hours a part throughout the day.

Circadian Rhythms .

Circadian rhythms correspond to the solar day (24 hours). These are most pervasive rhythms, regulating the temporal spacing and organization many even for every day in the lives of most living organism.

It is more natural for circadian rhythms to be synchronized to an external time giving stimulus than to exist in the free running state. In theory external time giving stimuli may be any rhythmically occurring events, for example, temperature, barometric pressure, gravitational change, or other cues that impinge on the organism.

In reality, however, only the external stimulus is important for most organism.

Lunar Rhythms are exemplified by the patterning of locomotor activity in fiddler crabs that, under constant laboratory conditions, exhibit an activity rhythms of 24 hours , 50 minute -the lunar day. The rhythms patterning of the crabs, activity is synchronized with daily low tides that are caused ultimately by the gravitational effect of the moon, although the laboratory has no water movements or light from the sun or the moon.

The Circannual Rhythms theoretically consist of a series of stages called interval timers. Each stage requires a fixed a mount of time and lead to the next stage.

In many species of animal a nerve pathway from the eye to region of the hypothalamus , the suprachiasmatic nuclei, allow light to exert internal synchronization. This region of the brain has been shown to be necessary for rhythmicity and entrainment of several forms of behavior. When the nuclei are destroyed, the rhythmic release of ACTH, an activating hormone from the pituitary stops. Thus, these nuclei appear to be at or near the top of the hierarchical control of bodily circadian rhythms, and they may be the site of predominant circadian rhythms clock in mammal, acting as a pacemaker for other body clock or biologist clock.