Suprachiasmatic nucleus: the internal clock of the brain

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 functions and unconscious. It is not simply the biological basis of the human intellect; it is also in charge of a multitude of essential processes for our survival.

The suprachiasmatic nucleus is an example of this.. While certain regions of the brainstem are responsible for enabling the heartbeat or regulating body temperature so that our cells do not die, this brain structure acts as our clock internal. Next we will see what exactly this means and what anatomical characteristics the suprachiasmatic nucleus presents.

• Related article: "Parts of the human brain (and functions)"

What is the suprachiasmatic nucleus?

We understand the suprachiasmatic nucleus to be a small structure made up of some 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 composed 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 lies above the optic chiasm, which is an area located at the base of the brain where optic nerves they intersect, 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, limiting both sides of the third cerebral ventricle.

The fact that the optic chiasm is situated just above the optic nerves is not accidental; 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 levels of activity of the body 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

In other words, the suprachiasmatic nucleus intervenes in the sleep-wake cycles, and makes us more prone to sleep in certain hours and waking up at others, for example, and that we do not have the same energy at 12 noon as after have dinner.

The cycles regulated by the suprachiasmatic nucleus last 24 hours, since evolution has made it adapt to the length of a calendar 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 longer, and it is delayed. the massive secretion of melatonin, a hormone that is much more numerous just before beginning to sleep and while we remain in the sleep phase.

• Related article: "Melatonin: the hormone that controls sleep and seasonal rhythms"

operating mechanism

When we look somewhere, the light that reflects what we are directing our eyes towards is projected on the retina, a layer of cells located inside the eye that some scientists consider part of the diencephalon

This membrane picks up 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 of most of this information passes through the thalamus and through 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 causes orders to be sent 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 is interpreted as the demands of the environment. Ultimately, if we are designed in a way that generates more efficiency during daylight hours, it is better take advantage of those moments and leave the hours of darkness to rest, according to the logic of the selection natural.

However, the use of artificial light sources can turn this against us and, for example, exposing ourselves to the light of a computer screen computer shortly before going to sleep gives us insomnia despite being tired from a long day of job. This makes our body try to respond to a strange situation for which it has not been prepared: days with much more daylight hours.