Suprachiasmatic Nucleus: The Brain’s Internal Clock
Although we often assume that the human brain is basically the organ that allows us to think and be aware of things, the truth is that it also performs all kinds of automatic and unconscious functions. It is not simply the biological basis of human intellect; It is also responsible for a multitude of processes essential for our survival.
The suprachiasmatic nucleus is an example of this While certain regions of the brain stem are responsible for enabling the heart to beat or regulating body temperature so that our cells do not die, this brain structure acts as our internal clock. Below we will see what exactly this means and what anatomical characteristics the suprachiasmatic nucleus has.
We understand the suprachiasmatic nucleus to be a small structure made up of about 20,000 neurons located in the area of the hypothalamus closest to the face, that is, in the lower part of the diencephalon. It is made up of gray matter.
It must be taken into account that there is a suprachiasmatic nucleus in each cerebral hemisphere that is, two per individual on each side of the head.
Your location
As its name indicates, the suprachiasmatic nucleus It is located above the optic chiasm, which is an area located at the base of the brain in which the optic nerves cross, passing to the opposite hemibody. It is also possible to locate it taking the hypothalamus as a reference, since it is located in the anterior part of this brain structure, bordering both sides of the third cerebral ventricle.
The fact that the optic chiasm is located just above the optic nerves is not coincidental; In fact, its operation has to do with the light signals that are captured by the retina, as we will see.
Functions of the suprachiasmatic nucleus
The main task of the suprachiasmatic nucleus is regulate circadian rhythms that govern the body’s activity levels depending on the moment in which we find ourselves. Circadian rhythms are the cycles that determine when there is a greater need to rest and when there is a large amount of energy available and therefore we will move more, think better, etc.
That is, the suprachiasmatic nucleus intervenes in the sleep-wake cycles, and makes us more likely to sleep at certain times and wake up at others, for example, and that we do not have the same energy at 12 noon as we do after dinner. .
The cycles regulated by the suprachiasmatic nucleus last 24 hours, since evolution has made it adapt to the length of a natural day from the luminosity captured through our eyes.
Thus, when we are exposed to light, this is interpreted by this brain structure as evidence that it is time to stay awake for longer, and it is delayed massive secretion of melatonin a hormone that is much more numerous just before starting to sleep and while we remain in the sleep phase.
Operating mechanism
When we look somewhere, the light that reflects what we direct our eyes towards is projected onto the retina, a layer of cells located inside the eye and which some scientists consider part of the diencephalon.
This membrane collects the electrical signals in which the light patterns of what we see are translated, and sends this information to the brain through the optic nerves. The usual route for most of this information passes through the thalamus and the occipital lobe, an area in which visual information begins to be integrated into larger and more complete units.
However, part of this information deviates from this route at the level of the optic chiasm, located at the “entrance” to the brain, to reach the suprachiasmatic nucleus. This structure does not recognize details of light patterns, shapes or movement, but is sensitive to the general amount of light that is being collected by the retinas. This sends orders to other areas of the body related to circadian rhythms, such as the pituitary gland, located nearby.
In this way, our body adapts to what it interprets to be the demands of the environment. Ultimately, if we are designed in a way that generates more efficiency during daylight hours, it is better to take advantage of those moments and leave the dark hours to rest, according to the logic of natural selection.
However, the use of artificial light sources This can turn against us and, for example, exposing ourselves to the light of a computer screen shortly before going to sleep can cause insomnia despite being tired from a long day of work. This makes our body try to respond to a strange situation for which it has not been prepared: days with many more hours of daylight.
