Distinction between circadian cycles and sleep?

In summary, biologists are surprised to observe sleep-like states in organisms with primitive nervous organization like in the freshwater polyps because they incorrectly assumed that sleep required a primitive central nervous system.
  • #1

Aidyan

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Semantic and technical distinction between circadian cycle and sleep.
Is, in biology, the notion of the circadian cycle (or rhythm) that one finds also in elementary forms of life (say a paramecium) the same notion of "sleep"? If not what is its technically difference? If it is, why are then biologist surprised to observed sleep-like states in organism with primitive nervous organization like in the freshwater polyps? https://pubmed.ncbi.nlm.nih.gov/33028524/
 
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  • #2
The paper is trying to answer: how did sleep evolve for animals with the first central nervous systems?
It is not making claims about other things, other than it makes assumptions - primarily that sleep requires a primitive central nervous system and if you find an "early" enough CNS you can learn about how sleep evolved.

Humans intuitively use "cubby hole systems" to classify things, Biologists are no different. So what you correctly observe is that Circadian cycles in living things are supposed to have existed before sleep.
What is halfway between the two? An as yet undefined (not seen) progenitor for sleep? What if they are all extinct?

Since these are definitions we apply, and living things do not care about our definitions, that breaks the cubby hole method - you need a half-way hole.
 
  • #3
But the statement that "Circadian cycles in living things are supposed to have existed before sleep" automatically implies that circadian cycles and sleep are two very different processes that one should distinguish. What distinguishes it? If there is no distinction, i.e. circadian cycle=sleep, then the assumption that "sleep requires a primitive central nervous system" makes no sense: it is a well known fact that already single cells undergo a circadian cycles.
 
  • #4
Bacteria can have circadian activity cycles of various kinds.
Circadian cycles are not limited to just sleep cycles.
Daily sleep cycles are a subset of circadian activity cycles.
Some other activity cycles involve nervous system activity, but not all.

Plants also have circadian cycles. No nervous system there.
 
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  • #5
It is a human perception/definition problem - not a problem in Nature -- was my point.
 

1. What is the difference between circadian cycles and sleep?

Circadian cycles refer to the natural rhythm of biological processes in our body that follow a 24-hour cycle, such as hormone production, body temperature, and sleep-wake cycles. Sleep, on the other hand, is a state of altered consciousness where our body and brain rest and repair.

2. How are circadian cycles and sleep related?

Circadian cycles play a crucial role in regulating our sleep-wake cycles. Our body's circadian rhythm influences our sleep patterns, with most people experiencing a natural dip in alertness and a peak in sleepiness during the night. In turn, getting enough quality sleep helps maintain a healthy circadian rhythm.

3. Can circadian cycles be altered?

Yes, our circadian rhythm can be influenced by external factors such as light exposure, eating habits, and work schedules. For example, frequent travel across time zones can disrupt our circadian rhythm, resulting in jet lag. Our circadian cycles can also be altered by certain medical conditions or medications.

4. How does technology affect circadian cycles and sleep?

The use of electronic devices with screens emitting blue light can suppress the production of melatonin, a hormone that helps regulate sleep. This can disrupt our circadian rhythm and make it harder to fall asleep at night. It is recommended to limit screen time before bedtime to promote better sleep.

5. What are the consequences of a disrupted circadian rhythm?

A disrupted circadian rhythm can lead to various health issues, such as difficulty falling asleep and staying asleep, daytime sleepiness, and fatigue. It has also been linked to an increased risk of obesity, diabetes, and cardiovascular disease. It can also affect cognitive function, mood, and overall well-being.

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