Ultradian rhythm, within chronobiology, denotes biological activities occurring in physiological cycles of 20 hours or less. They are usually independent of geophysical factors, except for circumambular rhythms (about 12 hours). They influence various animal behaviors, such as feeding, movement and exploration, as well as copulation, attentional level and learning. Its frequency in mammals is proportional to the metabolic rate, and inverse to the age of the animal in question.
The term descriptive ultradian is used in sleep research to describe individual states of sleep that occur within the intervals of the circadian cycle of the organism, and especially to refer to the ultradian cycle of 90-120 minutes of human sleep. > Some of the body's ultradian cycles are the release of hormones, heart rate, lung ventilation, thermoregulation, dilation of the nostrils and appetite. The latter involves the release of neuropeptide Y (NPY) and release of hormone corticotropin (CRH), stimulating and inhibiting the ultradian rhythms of appetite.
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