Biological Rhythms (OpenStax Psychology 2e)
Biological rhythms are internal rhythms of biological activity. A woman’s menstrual cycle is an example of a biological rhythm—a recurring, cyclical pattern of bodily changes. One complete menstrual cycle takes about 28 days—a lunar month—but many biological cycles are much shorter. For example, body temperature fluctuates cyclically over a 24-hour period (Figure 1). Alertness is associated with higher body temperatures and sleepiness with lower body temperatures.
This pattern of temperature fluctuation, which repeats every day, is one example of a circadian rhythm. A circadian rhythm is a biological rhythm that takes place over a period of about 24 hours. Our sleep-wake cycle, which is linked to our environment’s natural light-dark cycle, is perhaps the most obvious example of a circadian rhythm, but we also have daily fluctuations in heart rate, blood pressure, blood sugar, and body temperature. Some circadian rhythms play a role in changes in our state of consciousness.
If we have biological rhythms, then is there some sort of biological clock? In the brain, the hypothalamus, which lies above the pituitary gland, is a main center of homeostasis. Homeostasis is the tendency to maintain a balance, or optimal level, within a biological system.
The brain’s clock mechanism is located in an area of the hypothalamus known as the suprachiasmatic nucleus (SCN). The axons of light-sensitive neurons in the retina provide information to the SCN based on the amount of light present, allowing this internal clock to be synchronized with the outside world (Klein, Moore, & Reppert, 1991; Welsh, Takahashi, & Kay, 2010) (Figure 2).
Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020). Psychology 2e. OpenStax. Houston, Texas. Accessed for free at https://openstax.org/details/books/psychology-2e
Date Published: June 10, 2010 Publisher: Public Library of Science Author(s): Sufang Zhang, Jianing Wei, Xiaojiao Guo, Tong-Xian Liu, Le Kang, Shin Yamazaki. http://doi.org/10.1371/journal.pone.0011064 Abstract: In a tritrophic system formed by a plant, an herbivore and a natural enemy, each component has its own biological rhythm. However, the rhythm correlations among the three levels and the … Continue reading
Research Article: Temperature–amplitude coupling for stable biological rhythms at different temperatures
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Research Article: Milk Leptin Surge and Biological Rhythms of Leptin and Other Regulatory Proteins in Breastmilk
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Research Article: Diurnal Rhythms in Neurexins Transcripts and Inhibitory/Excitatory Synapse Scaffold Proteins in the Biological Clock
Date Published: May 25, 2012 Publisher: Public Library of Science Author(s): Mika Shapiro-Reznik, Anje Jilg, Hadas Lerner, David J. Earnest, Nava Zisapel, Michael Hendricks. http://doi.org/10.1371/journal.pone.0037894 Abstract: The neurexin genes (NRXN1/2/3) encode two families (α and β) of highly polymorphic presynaptic proteins that are involved in excitatory/inhibitory synaptic balance. Recent studies indicate that neuronal activation and memory … Continue reading