Why do we sleep? From an evolutionary point of view, such a vulnerable period of time should not have fayred for this length of time. Many fitness trackers these days will show how much time is spend in each stage but what does that really mean? Why is it sometimes I think I sleep well and then I see my tracker and it tells me my score is 50 which would fully ruin my day. Why is it that melatonin, a hormone that drives sleep doesn’t actually make me fall asleep if I am to use it?
We usually have different cycles of sleep that last around 90 minutes each, so overall an individual might go through 4-6 rounds of sleeping. The stages can be split into NREM and REM sleep.
NREM (3 stages)
Stage 1 or N1: Light Sleep
Stage 2 or N2: Light Sleep
Stage 3 or N3: Deep Sleep
REM (1 Stage)
REM Sleep
N1 Sleep → quite easily awoken in this stage
N2 Sleep → more relaxed state and body temp starts to drop (majority of the night is spent in this phase)
N3 Sleep → hard to wake someone in this phase (this is when growth hormone is released and immune function is bolstered). Usually more in the first half of the cycle
N4 Sleep → usually when you have vivid dreams (have muscle paralysis apart from eyes and muscles that control breathing). Helps with memory/learning/creativity. REM sleep usually occurs more during the second part of the night
Cellular level
Sleepiness - it seems that this is driven by GABA-A and Adenosine.
Wakefulness - dopamine/noradrenaline/serotonin/histamine
Circadian rhythms are 24 hour rhythm cycles that govern the timing of the release of many of hormones and many of the neurotransmitters that have been mentioned.
We know that we have a 24 hour rhythm from the Siffre experiments, where he went into a cave to record his experiences and it was found that he was still able to identify how long one day was. We need the morning light exposure to essentially sync our own circadian rhythm with the earth’s cycle so we can I guess be most productive
Andrew Huberman talks all about this early morning light exposure but I always took this at face value, what does the evidence have to prove this.
From what I can gather, you can augment the wakefulness hormones including the dopamine, noradrenaline, serotonin and the cortisol awakening response which can improve focus and attention.
Blue light hits the retinal ganglion cells which go to the SCN in the hypothalamus.
In the SCN, there is modification of the clock genes which sends timing signals to the rest of the body. SCN also releases the melatonin when there is less blue light.
On top of this system, there is also the adenosine that builds up as it is a by product of being used as ATP from energy so this is quite natural.
My question then would become why not just give adenosine - but the dose is the poison