4. Distinguish between diurnal, circadian and free�running rhythms.
Diurnal rhythms are biological rhythms that occur within a 24-hour period, typically following a daily cycle. Many physiological processes, such as sleep-wake cycles, body temperature, hormone secretion, and certain behaviors, exhibit diurnal rhythms. These rhythms are influenced by external cues called zeitgebers, mainly the light-dark cycle.
Circadian rhythms, on the other hand, refer to the body's internal biological clock that controls various physiological and behavioral processes in a 24-hour cycle, even in the absence of external cues. The term "circadian" comes from the Latin words "circa" (around) and "diem" (a day), emphasizing the inherent 24-hour nature of these rhythms. While circadian rhythms can be influenced by external cues such as light and social interactions, they persist even without these cues, making them endogenous processes.
Free-running rhythms are a specific type of circadian rhythm where an organism's biological clock is not influenced by external cues. In a completely isolated environment without any external time cues, such as artificial light or social interactions, an organism with a free-running rhythm would exhibit a consistent cycle that is not necessarily synchronized with the natural 24-hour day. This can lead to deviations from a typical sleep-wake cycle, hormone secretion, and other physiological processes. Studying free-running rhythms can help understand the inherent biological timing mechanisms within organisms.
Diurnal, circadian, and free-running rhythms are all related to biological patterns and are influenced by the Earth's rotation and other environmental cues. However, there are key differences between these rhythmic patterns. Here's a step-by-step breakdown:
1. Diurnal Rhythms:
- Diurnal rhythms are biological patterns that follow a 24-hour cycle, corresponding closely to the Earth's rotation.
- They are commonly linked to the sleep-wake cycles and daily activities of animals, including humans.
- Diurnal animals are typically active during daylight hours and rest or sleep during the night.
2. Circadian Rhythms:
- Circadian rhythms are also biological patterns that repeat roughly every 24 hours, but they are internally controlled by an organism's biological clock.
- These rhythms persist even in the absence of external cues, such as light-dark cycles.
- Circadian rhythms regulate various bodily functions, including sleep-wake cycles, hormone production, body temperature, and metabolism.
- They are found in both diurnal and nocturnal organisms, reflecting their natural behavioral and physiological fluctuations over a 24-hour period.
3. Free-Running Rhythms:
- Free-running rhythms occur when an organism's biological rhythms are not synchronized or entrained to external cues, such as light-dark cycles.
- This can happen when an organism is isolated from external time cues or when their biological clock is not functioning properly.
- In free-running conditions, an organism's internal biological rhythms may not align with the 24-hour day, leading to a unique pattern of activity/rest cycles.
- Free-running rhythms can deviate from the diurnal or circadian patterns, making it challenging for individuals to maintain regular sleep-wake schedules.
In summary, diurnal rhythms follow a 24-hour cycle corresponding to the Earth's rotation, circadian rhythms are internally controlled patterns influenced by an organism's biological clock, and free-running rhythms occur when an organism's biological rhythms are not synchronized with external cues.