Circadian rhythms

Summary

This lesson in biopsychology delves into the intricacies of biological rhythms, distinguishing between Circadian, infradian, and ultradian rhythms. It explores the interplay of endogenous and exogenous factors in regulating the sleep-wake cycle, with a focus on the role of the suprachiasmatic nucleus and melatonin. The lecture examines the implications of these rhythms on health and behavior, including the effects of desynchronization in shift workers and the use of light therapy for seasonal affective disorder. It also highlights the individual variability in circadian rhythms and the methodological challenges in studying them.

Takeaways

• 🕒 Biological rhythms are periodic cycles that occur at regular frequencies, with Cadian rhythms happening once every 24 hours, infradian less than once, and ultradian more than once.
• 🌓 Endogenous refers to internal body clocks, while exogenous refers to external factors that influence our rhythms, such as light, social cues, and meal times.
• 🔄 Entrainment is the synchronization of external and internal factors, highlighting the interaction between nature and nurture in regulating biological rhythms.
• 🌡️ Core body temperature is an example of a Cadian rhythm, with the lowest at 4 a.m. and the highest at 6 p.m., affecting alertness and cognitive ability.
• 💉 Hormones like cortisol follow a Cadian rhythm, peaking in the morning to help with stress response and alertness, and lowest in the middle of the night.
• 🌙 Melatonin and growth hormone peak at midnight, aiding in body restoration and growth, demonstrating the importance of sleep for overall health.
• 🛌 The sleep-wake cycle is a focus of the lesson, questioning whether our natural cycle is 24 hours or influenced by societal norms and external cues.
• 🧠 The superchiasmatic nucleus (SCN) in the hypothalamus is crucial for the sleep-wake cycle, receiving light information and signaling the pineal gland to produce melatonin.
• 🐹 Studies on animals, such as transplanting the SCN in hamsters and removing it in chipmunks, show the evolutionary importance and internal regulation of Cadian rhythms.
• 🕳️ The 'caveman' study, where an individual lived in isolation without external cues, revealed a natural tendency towards a slightly longer than 24-hour cycle.
• 💡 Light is a significant exogenous factor, affecting the sleep-wake cycle even when not perceived through the eyes, with implications for phototherapy and treating conditions like Seasonal Affective Disorder.

Q & A

What are the three main types of biological rhythms mentioned in the script?

The three main types of biological rhythms are Circadian, infradian, and ultradian rhythms. Circadian rhythms occur once every 24 hours, infradian rhythms occur less than once every 24 hours, and ultradian rhythms occur more than once every 24 hours.

What does the term 'endogenous' refer to in the context of biological rhythms?

Endogenous refers to the internal body clock, which is the internal mechanism within an organism that influences its biological rhythms.

What is the role of the exogenous factors in the sleep-wake cycle?

Exogenous factors are external to the body and can influence the sleep-wake cycle. These factors include the time of day, the presence or absence of light, social cues, and meal times.

What is the concept of entrainment in relation to biological rhythms?

Entrainment refers to the synchronization of external and internal factors. It is the process by which an organism's internal clock becomes aligned with external cues, such as light and dark cycles.

Can you provide an example of a Circadian rhythm other than the sleep-wake cycle?

An example of a Circadian rhythm is the core body temperature, which has its lowest point around 4:00 a.m. and its highest around 6:00 p.m.

What is the significance of the hormone cortisol in relation to the sleep-wake cycle?

Cortisol is a hormone that helps in the stress response and alertness. It is lowest in the middle of the night and starts peaking in the morning, preparing the body to deal with the day's demands.

What is the role of the superchiasmatic nucleus (SCN) in the regulation of the sleep-wake cycle?

The superchiasmatic nucleus (SCN) in the hypothalamus is responsible for receiving light information from the eyes and sending signals to the pineal gland to produce melatonin, which induces sleepiness in the absence of light.

What did the study involving the transplantation of the SCN in hamsters reveal about the role of the SCN in Circadian rhythms?

The study showed that the SCN is the main initiator of the Circadian rhythm, as the transplanted SCN from hamsters with a 20-hour sleep cycle into normal hamsters resulted in the 20-hour cycle being adopted by the recipients, demonstrating the SCN's influence over the rhythm regardless of external factors.

What was the outcome of the study involving the removal of the SCN in chipmunks?

The removal of the SCN in chipmunks resulted in a complete disruption of their Circadian rhythm, leading to irregular sleep patterns and an increased vulnerability to predators, highlighting the evolutionary importance of maintaining natural biological rhythms.

What are some practical applications of understanding the effects of endogenous and exogenous factors on the sleep-wake cycle?

Practical applications include using light therapy for treating Seasonal Affective Disorder, synchronizing medication schedules with the body's rhythm for better pharmacokinetics, and using melatonin supplements to help blind patients establish a 24-hour sleep-wake cycle.

What are some methodological issues or considerations when evaluating studies on biological rhythms?

Methodological issues include the individual differences in Circadian rhythms, the lack of population validity due to unique cases like the cave study, and the fact that conclusions drawn may not be reliable over time or across individuals due to factors like age and personal preferences.