Ultradian rhythm

A biological rhythm is called ultradian when its period is shorter than 24 hours. Thus it differs from the Circadian rhythm with the approximate period length of one day and the infra Circadian rhythm with a period longer than one day.

Research on Ultra Circadian rhythms are expected to chronobiology. Ultradian rhythms were observed in physiological functions, such as cellular processes, respiration, circulation, release of hormones and sleep phases. They also occur in behavior and especially food intake cycles.

Ultradian rhythms characterized by a great diversity not only in the period length ( from hours to milliseconds), but also in function and mechanism.

Examples of regularly recurring events ultradian

Ultradian oscillations are assumed for all biological systems and can be, down to cell or bacteria level evidence. Typical examples of ultradian processes in biology are the heart action, breathing and pulsatile release of hormones in animals and humans. Also regularly repeating leaf movements in plants and cell division rhythm in eukaryotes can be included.

Important biochemical oscillations at ( yeast) cell extracts in the form of synchronous observed. Synchronous ultradian rhythms occur in glycolysis of yeast cells, the allosteric enzyme phosphofructokinase plays a key role in this case. The striking clusters of similar cell cycles in populations of ciliates and amoebae are stable ultradian and temperature compensated mechanisms underlying.

Another important example of ultradian rhythms is the exchange of the various sleep stages ( eg REM - NREM cycle). One cycle takes about 1.5 hours. Furthermore, even in the daytime ultradian a rhythmic fluctuations in human performance can be observed.

The time interval between the individual food intakes also corresponds to an ultradian rhythm. Especially for herbivorous birds and mammals periodic processes such as rumination and coprophagy are observed. Is particularly pronounced ultradian rhythms in many insectivores and rodents.

The research in recent years could prove rhythmic biochemical processes at the cellular level as the controlling mechanisms. The under the control of so-called clock genes related to self-inhibiting biosynthesis of proteins is one of the molecular " clock " mechanisms. In some of these operations, a temperature compensation could be observed, which means that the corresponding rhythmic process not or hardly depends on the temperature. Lesion studies could show that the area of the suprachiasmatic nucleus, where the controller entity is localized for circadian processes in most mammals (the endogenous clock of man), is not responsible for the emergence of ultradian rhythms. Another area ( caudal to the suprachiasmatic nucleus - ie spatially behind it) appears to play a role, however.

• Chronobiology