Sleep 8.6 Understanding Process C and S in Sleep Regulation

Name: Sleep 8.6 Understanding Process C and S in Sleep Regulation
Uploaded: 2025-11-25T12:14:31.659Z
Duration: 5:32
Description: How these systems interact, how sleep deprivation alters non-REM sleep, and the role of hormones like melatonin, cortisol, growth hormone, and prolactin.

How these systems interact, how sleep deprivation alters non-REM sleep, and the role of hormones like melatonin, cortisol, growth hormone, and prolactin.

Video Breakdown:

00:00 Introduction to Process C and S

01:27 Homeostatic Mediators and Their Effects

02:12 Sleep Homeostasis and Sleep Deprivation

03:02 Hormones Associated with Process S

03:55 Distinguishing Process C and Process S

05:08 Conclusion: Interaction Between Process C and S

Now finally, quickly going through Process C and S.
So Process C here is demonstrated by these cyclical changes. It gives us the alertness throughout the course of the day. So you could see that this is the time period of sleep. During the day you could see that you get more alert, and during the night you get less alert. Now, Process S or homeostatic process of sleep regulation is more sensitive throughout the course of the day.
So as you're more active, you start to get more and more tired. And then at some point you have an accumulation of some kind of metabolite that then leads to this increased sleepiness that then subsequently meets up with this sleep threshold and this causes you to go to sleep. And so, when you go to sleep, that metabolite or your energy sort of metabolite gets reduced and your energy increases and it's ultimately you reach the waking threshold and so you reset through the day. Now, if you take a nap, those metabolites can reduce, and so, when you go to sleep, you're able to, as well go to sleep, but then it meets this waking threshold a little earlier, so you could potentially wake up earlier.
Now, if you also do an all-nighter, you have the accumulation of metabolites, and so you're way above the sleep threshold, so you're gonna be feeling sleepy throughout the the day. And so what are those homeostatic mediators? There's plenty evidence to suggest that adenosine is that mediator.
It's a byproduct of metabolic activity, it rises during the wake and falls during sleep, and it influences our sleep regulatory parts of the brain, which is the VLPO. Caffeine basically mediates the activity through adenosine because it competes with the adenosine A1 receptor.
So you're feeling less tired because the brain's not sensing the adenosine. Cytokines can also affect the Process S and this is why when you're sick, you reproduce these cytokines that then subsequently affect the VLPO, and cause you to feel more sleepy. I wanted to quickly show how sleep homeostasis works, particularly during an after sleep deprivation. So in panel A, we see the percentage of non-REM sleep across time. And so during the normal baseline day you have non-REM, so this is during sleep, you see the non-REM percentage high, and then when you wake up, the non-REM percentage decrease.
And you can see the slow wave activities sort of stay the same. However, if you're deprived of sleep and then you go to sleep again, there's a little bit of a rebound effect and Process S mediates this. You can see that the non-REM increases, and particularly the slow wave activities increase right after you go to sleep.
So it's a way in which our body compensates for the sleep debt that occurs. Which hormones are associated with Process S? This is an interesting study that did hypnosis before a a nap and then there's a control group who didn't get the hypnosis and there was a number of data that were recorded across this experiment.
And you could see here that the slow wave sleep in those individuals who got hypnosis got a great quality of sleep. So they got more slow wave sleep and had a deeper stage of sleep according to S4 and S3. And then you could see that the corresponding changes, so you have increase in growth hormone for those people who got more slow wave sleep activity and you also increased prolactin levels as well, whereas cortisol really didn't have any changes.
So the hormones that are associated with Process S is growth hormones and prolactin. And so to distinguish the Process C and Process S, Process C is an anticipatory process. It affects nearly all the tissues. Remember the how melatonin, cortisol, and temperature affects all the tissues. And what it does it, it primes the terrain for the next stage of diurnal activity.
Process S on the other hand, is reactive. It affects very specific, pertinent tissues, like growth hormone doesn't affect all tissues of the body and in response to the prior state for optimal restoration or growth. So if you've gotten sufficient nutrition in the previous day, then the growth hormone if you're trying to grow, will be more active.
Or if you are sick, then you'll get more sleep, as a result of Process S. And so the hormones responsible for Process C, melatonin, cortisol, and through cortisol, ADH and the Renin Angiotensin System hormones. For Process S involves growth hormones, testosterone, prolactin, and then the autonomic nervous system for Process C sets the baseline rhythm.
And for Process S, it modulates the phasic shifts. So PNS is maximal during the non-REM sleep. And so the key synthesis here is that processes sets the scaffold and processes superimposes state dependent modulation. So these are the two, the how these two interact with each other.

Course episodes

Sleep 8.1 Introduction to Circadian Physiology

Sleep 8.2 The Suprachiasmatic Nucleus: The Body’s Master Clock

Sleep 8.3 Peripheral Clocks: Synchronizing the Body Beyond the Brain

Sleep 8.4 Systemic Zeitgebers: How the SCN Coordinates the Body

Sleep 8.5 Non-Photic Zeitgebers: Meal Timing, Exercise, and Metabolism

Sleep 8.6 Understanding Process C and S in Sleep Regulation