Below the picture is great information on biological clocks. As a result of the activity of internal clocks, the behavior patterns of many living things show distinct rhythms. There are three possible results Periodicity ceases - the regular changing behaviour pattern stops Periodicity continues with a pattern of almost exactly 24 hrs Periodicity continues but varies from the 24 hr pattern by a constant amount. This type of periodicity is said to have a spontaneous frequency . The length of the period is called the free running period and is generally very precise.
Clocks are also present in hormone mechanisms and brain structures.
The human biological clock is made up of paired nuclei which are small pieces of tissue in the brain about 0.3mm in size. It is located just behind the eyes where light stimulates nerves that connect with the clock and reset it. The SCN works by telling the pineal gland to begin or cease production of the sleep inducing hormone melatonin. Darkness starts production while light shuts it off. Copyright 2000 Jesse Gerulis .