Biological Rhythms

Ultradian Rhythms

Ultradian rhythms are the most frequent and occur more than once in 24 hours.

Examples

• Eating.
• Going through the 5 stages of sleep several times each night.

Circadian Rhythms

Circadian rhythms occur about ("circ") once a day ("dia").

Earth turns in a circle = day.

Examples

• Sleep-wake cycle.
• Daily fluctuation in body temperature.

Infradian Rhythms

Infradian are the most "infrequent". They occur less than once a day.

Examples

• Menstrual cycle.
• Season affective disorder (SAD - yearly cycle of depression starting in the winter).
• Hibernation.