The science of sleep raises one of the most complex issues of Neuroscience; namely what it means to be awake or asleep.
Since neurology approaches the science of sleep as a different state of awareness, let’s see what the research has contributed to our understanding of sleep.
Without doubt, our brain structure is extremely complex but the structure relating to sleep is off the charts.
Both states, awake and asleep, are actively induced by certain areas of brain. That means it is controlled by the brain, not the soul and not the conscious mind. The science of sleep all comes down to brain chemistry.
In cell physiology, a nucleus is the central structure of the cell and in atomic science, a nucleus is the central structure of the atom. In neurology, a lot of talk is centered on a nucleus or the plural nuclei but it means something entirely different.
In neuroscience, a nucleus is a collection of neuron cell bodies organized into a structure having a unique cytoarchitecture, connections and function. Cytoarchitecture is a physical trait that refers to how neurons are arranged in groups or layers.
Now that we have all that straight, let's consider the brain architecture that controls sleep. Two major areas come into play for sleeping and dreaming.
As to location, the first involves nuclei found at the pons and midbrain junction. The diagram below shows the locations of these structures. The other involves nuclei in the pons, medulla and others that project into the cortex.
Here's the significance. Examinations into the science of sleep show that both of these systems are turned on and remain active while we are awake.
As we fall asleep and progress through the sleep stages, there is a decrease in activity of both systems and when we hit the REM stage, the first system is highly active and the second is completely turned off.
So far, so good. Now we put names with these systems and see how they relate to the science of sleep.
The first is called the reticular formation, consisting of 110 different nuclei, and extending from the lower parts of brain to the fore-brain. Specific nuclei in the reticular formation play a critical role and they are controlled by another structure of the brain, the hypothalamus.
The hypothalamus is associated with maintaining homeostasis in the body, meaning balance or proper functioning. Just from seeing the name "hypothalamus", we could assume that it is located below the thalamus, which it is.
Regarding the science of sleep, the hypothalamus regulates the light/dark cycle, sometimes referred to as a circadian rhythm.
"Circadian" means a day, thus a circadian rhythm is a complete day and obviously is divided into two parts; the day (light) part and the night (dark) part.
since we now know what a nucleus in the brain is, we can say that there is a special nucleus in the hypothalamus, called the Suprachiasmatic nucleus.
This is the nucleus that is the "doorway" of circadian rhythm regulation. Why the doorway? Because it gets a direct input from the eye, the retina.
The eye knows when it’s light or dark and directly transmits the information to the suprachiasmatic nucleus.
Why in the world would anyone name a pea-sized brain nucleus "suprachiasmatic"? It turns out that sometimes these Latin and Greek names really do mean something.
Supra means "above", chiasm is Greek for "crossing" so someone
decided to name this little guy the "suprachiasmatic nucleus" because it is located "above" the point where the optic nerves "cross".
For you all who care about such things, the right eye optic nerve crosses over to the left brain and the left eye optic nerve crosses over to the right brain.
We can't leave the science of sleep without mentioning the pineal gland. This is an endocrine gland that produces melatonin, a hormone involved in the sleep/wake cycles.
The wrap up message is that all these nuclei are involved in very complex circuits that control waking, sleeping, dreaming & switching and all the workings are actively induced and maintained by the brain.