2023-04-30 20:00:00
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On 30.04.2023 at 10.00 a.m.
Modified on 30.04.2023 at 22:00
The sleep/wake cycle is the result of several intertwined physiological processes in the brain.
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L’The technical epicenter of sleep is well sheltered in our cranium. The brain, it is him in question, weighs his weight, approximately 1.3 kg, and it is covered with three protective envelopes, the meninges. Very vascularized, it consumes a lot of oxygen and glucose is its main dish. At the structural level, it is a complex piece of machinery made up of several “parts”, like a car engine.
Neurotransmitters, genetics, light and social life “make sleep”
At the cellular level, the brain is traversed by multiple networks of neurons which secrete chemical substances and react to them, it is the neurotransmitters (or neuromediators): histamine, hypocretin, norepinephrine and acetylcholine which participate to the wakefulness system, serotonin which plays on both counts, wakefulness and sleep, GABA (gammaaminobutyric acid), inhibitor of the wakefulness system. The subtle mechanics of sleep thus depends on five arousal systems which interact with each other: it is their standby which triggers sleep, also favored by the accumulation in the brain of adenosine, produced by the neurons, until to a threshold that eventually inhibits brain activity. The genetic factor also comes into play, as shown by astonishing studies, in particular on the sleep of twins. It is these different levels of functioning that “make” sleep, in relation to exogenous stimuli such as light and social life..
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Fall asleep
The ventrolateral preoptic nucleus (VLPO), located at the front of the hypothalamus, is a pinhead-sized group of cells that work while we sleep. Indeed, it blocks the arousal systems, which are also inhibited by the accumulation of adenosine. Caffeine and theine keep us awake because they oppose the action of adenosine.
Wake
The suprachiasmatic nucleus (SCN) is a small group of cells, approximately 1 mm3, located above the optic chiasm (the part of the brain where the two optic nerves cross), which reacts to the perception of light, intense or low. Its action is at the heart of the functioning of the circadian rhythm. Awakening systems interact with the VLPO according to the “flip-flop switch” model, which takes the image of the electric switch: when they “turn on”, they “turn off” the VLPO, responsible for sleep , and vice versa.
Focus on the workings of the brain
Cerebral cortex
It is activated during REM sleep by signals emitted by the bridge.
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The bridge
It is involved in the activation of dreams and in awakening. It blocks the signals sent to the spinal cord when we dream to prevent us from making uncontrolled movements.
Thalamus
It transmits when awake or blocks during sleep the information of the senses, which allows the brain to activate or deactivate.
Hypothalamus
Located in the center of the brain, it is a set of nuclei that regulate the body’s basic needs (eating, drinking, keeping warm). It contains two neural networks, the VLPO and the NSC, which interact and alternate wakefulness and sleep.
Pineal gland
It is she who produces during the night melatonin, this hormone that promotes sleep.
Seahorse
It is essential for memory formation. It replays the memories so that they are memorized during the phase of REM sleep.
Retina
There are melanopsin ganglion cells that send an arousal signal to the brain when they perceive light.
Thanks to Dr. Marc Rey, neurologist, president of the National Institute of Sleep and Vigilance (INSV).
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