Suprachiasmatic Nucleus: our Circadian Sleep-wake Center

The suprachiasmatic nucleus is for the neuroscientists the “master watchmaker”. Thanks to it our circadian rhythms are regulated. Any alteration in this area leads to insomnia and memory loss.

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The suprachiasmatic nucleus is located in the anterior region of the hypothalamus and contains about 20,000 neurons. Its function is as fascinating as it is decisive: it works as our internal clock regulating the sleep and wake cycles. Thus, and thanks to the stimuli that it receives through our retina, it allows us to be more or less active depending on the moment of the day in which we find ourselves.

People, like animals, are sensitive to the changes that occur in our environment. The Earth and its rotation establishes those patterns of light and temperature that condition our level of activation. All this facilitates our adaptation. Hence, that our metabolism is, in a way, intimately linked (although sometimes it may not seem) to nature.

These circadian rhythms are in turn mediated by what are, surely, the most interesting areas of our brain. In this way, regions -like the suprachiasmatic nucleus- become those regulatory “centers” capable of orchestrating precise neuronal and hormonal events to control aspects such as rest, energy, body temperature or hunger.

Let’s see more information about it.

“Look deeply into nature and then you will understand everything better.”

-Albert Einstein-

Suprachiasmatic nucleus: location and functions

Actually, we do not have a single suprachiasmatic nucleus. We have two, and both are located in each cerebral hemisphere and very close in turn to the hypothalamus. Likewise, they are integrated just above the optic chiasm with a very specific purpose: to receive the signals captured by the retina to regulate a large number of biological processes.

On the other hand, studies such as that published in the journal Frontiers in Neuroscience by Dr. Joseph L Bendot do not hesitate to call the suprachiasmatic nucleus the brain watchmaker. Even more, it is known that this brain structure favors such important processes as memory and learning. Enjoying an adequate and restful rest is still essential for our brain and each of its processes.

Thus, any dysfunction of the circadian system is related to diseases ranging from sleep disorders to memory loss (especially severe in the elderly).

How does the suprachiasmatic nucleus work?

The functioning of the suprachiasmatic nucleus is complex. The biochemical processes they put into operation are as precise as they are complicated. However, we can understand their development more easily if we divide them into steps:

  • This area receives information about ambient light through our retina.
  • The retina does not have only photoreceptors with which to distinguish shapes and colors. It also integrates ganglion cells, rich in a pigment type called melanopsin.
  • This pigment and its cells carry information directly to the suprachiasmatic nucleus.
  • Later, after analyzing the information received, send signals to the upper cervical ganglia for the pineal gland or epiphysis, secrete or inhibit the production of melatonin.
  • If it is night and there is no stimulation of sunlight, the secretion of melatonin will increase to reduce the level of activation and promote sleep.
    retina connected to the suprachiasmatic nucleus
  • The suprachiasmatic nucleus is the master of the rest of our “internal clocks”.

It has been a few decades since scientists are discovering more data about this structure thanks to the Drosophila fly. As we all know, this insect and its study are offering us valuable information on fundamental principles of biology and genetics.

At present, we know that the suprachiasmatic nucleus helps us to maintain circadian rhythms by coordinating the synchronization of many other internal “circadian clocks”. Because beyond what it may seem, both our body and the brain have hundreds of mechanisms that regulate infinite processes and behaviors.

The processes that would help to regulate would be the following:

  • The feeling of hunger
  • The digestive processes.
  • It favors hibernation in animals.
  • It regulates our body temperature.
  • It also regulates the production of hormones, such as growth hormone.
  • It encourages the brain and our body to carry out maintenance and restoration tasks. It does it during the REM phase.

Alterations of the suprachias nucleus

The functioning of the suprachiasmatic nucleus can be altered by many factors. Many of them derive from our habits of life:

  • Be awake at night in front of our electronic devices.
  • Do not follow a fixed routine in our schedules.
  • The jet lag.
  • Live in cities with a high degree of pollution.

In addition, the suprachiasmatic nucleus has a direct relationship with the pituitary and with the production of melatonin. As we can guess, it is common that, as we get older, the levels of this hormone decrease. All this leads to sleep disturbances, fatigue, loss of memory, exhaustion, discouragement, etc.

Likewise, it has also been seen that neurodegenerative diseases, such as Alzheimer’s, lead to a progressive loss of the neurons that make up the suprachiasmatic nucleus.

Therefore, let’s try (as much as possible) to take care of our routines. Ideal if we start to follow a schedule that does not have too many variations, regulating in a special way the exposure to the blue light of our devices.