Periodic Trends: Circadian rhythms ‘spring’ into action

Graphic by Kathryn Messinger

Graphic by Kathryn Messinger


Spring has officially begun and daylight saving time has past. If you have a night class, maybe it feels completely different now that you’re working in some daylight. The “winter blues” is not a myth. In fact, this kind of fatigue, mood imbalance and sleep disturbance can be related back to our natural circadian rhythms. All of our brains have natural “body clocks.” Even plants have circadian rhythms.

Circadian rhythms play a role in an organism’s ability to measure and interpret the “length” of a day. We’re all familiar with the fact that in the winter, the “day” is short and in the summer, the “day” is longer. The sun sets earlier in the winter and that means less light for us while we’re awake. The rhythm is linked to the light–dark cycle. Photoperiodism, the physiological response of organisms to the length of day or night, is vital to both plants and animals. Circadian rhythms affect sleeping and eating patterns while influencing body temperature, production of hormones, brain wave activity, heart rate, cell regeneration (such as red blood cells) and other biological functions.

Evolutionarily, an organism’s ability to predict seasonal periods is important when its survival is dependent on weather conditions, food availability or predator activity. Day length is also an important environmental cue for the seasonal timing of behaviors like migration, hibernation and reproduction.

The primary circadian “clock” in mammals is located in the suprachiasmatic nuclei, groups of cells found in the hypothalamus. Without these cells, there can be no proper sleep-wake patterns. The SCN receives information about light through the eyes. The retina in the eye has special cells that are linked directly
to the SCN.

Regulation of the hormone melatonin comes from the pineal gland in the brain. The pineal gland gets its information about the lengths of the day and night from the SCN. Secretion of melatonin is highest at night and is important for sleep. Measuring these levels is one main way scientists recognize the phases and timing of circadian rhythms.

Disturbance to the circadian rhythm can result in some health problems and can be used as a symptom for diagnosis of bigger concerns. Disruption of the circadian clock or non-synchronized circadian timing with the light-dark cycle plays a role in the development of metabolic disorders.

A number of other disorders, like bipolar disorder, jet lag and some sleep disorders, are associated with irregular circadian rhythms.

When our access to natural light becomes limited, our body clocks or circadian rhythms are directly affected. This results in changes in alertness, waking, sleeping, emotion and appetite. Moreover, artificial light does not have the same effect as light from the sun. Different wavelengths and spectra of light are perceived differently by the eye.

So if you’re feeling tired of all this snow and terrible, cold hikes to class, don’t worry. Our body clocks and increasing exposure to light will have you feeling alert and cheerful soon enough.

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