This part of the medulla oblongata helps us breathe continuously and automatically.
As a general rule, in a state of rest an adult human being breathes at a rate of between twelve and eighteen breaths per minute. Breathing is essential for our survival, a process that we carry out in a semi-conscious way continuously throughout our lives.
But who is responsible for us to do it? What part of our body causes us to carry out this basic function? The answer is found in the medulla oblongata, specifically in the preBötzinger complex.
The preBötzinger complex: description and basic location
The preBötzinger complex is a set or network of neurons located in the medulla oblongata or medulla oblongata, specifically in its ventromedial part, forming part of the brainstem. This neural network appears in both hemispheres, being a bilateral and symmetric structure. Connecting with the spinal cord, and as we have commented, it is fundamental for the generation and maintenance of the respiratory rhythm.
It is a recently located structure, specifically in 1991, and in it different types of neurons have been found that allow the genesis and rhythmicity of the respiratory cycle through their interaction. The preBötzinger complexes in both hemispheres appear to function partially independently, although they communicate in order to synchronize.
Although this structure is still little known, various functions of great importance are attributed to it.
1. Basic respiratory rhythm
The preBötzinger complex is a fundamental element to keep us alive, and its injury can cause death due to respiratory depression. Its main function is the generation and management of the respiratory rhythm.
2. Adequacy of respiration to environmental needs
The interaction with other areas of the brain enables the preBötzinger complex to regulate the respiratory rhythm based on environmental needs. For example, if we do sports, our breathing will accelerate.
3. Capture the oxygen level
It has been found that this complex and its connections are capable of detecting and acting according to the oxygen level in the body. For example, if we are suffocating, it is common for our respiratory rate to accelerate, since the body seeks to acquire the oxygen necessary to survive.
An unknown mechanism of action
The way in which this structure works is still not totally clear, but through experiments with rodents it has been shown that it is linked to the receptor, the hormone neurokinin-1 and to the action of neurotransmitters.
The existence of “pacemaker” neurons has been observed (in a similar way to what happens with heart rhythm), some voltage-dependent and others independent of it. Its exact operation is still debated, although it is speculated that the voltage-dependent ones are the ones most linked to the generation of the respiratory rhythm by allowing the emission of action potentials through sodium uptake.
In any case, the hypothesis with the greatest empirical support is the one that indicates that it is the action of the set of neurons and their interaction that allows the rhythm to be generated, being the result of the interaction and not of the activity of a single type of neuron.
Much more research is needed in this regard to know the exact functioning of this region, being a field of study to be deepened.
Regarding the neurotransmitters with the greatest effect in this area, it has been perceived that glutamatergic activity is essential for the pre-Bötzinger complex to act allowing respiration. Specifically, it is the activity of AMPA receptors that plays the most role, although some participation of NMDA receptors is also observed in the process (despite the fact that in some studies the modification of NMDAs did not generate real changes and they seem not to essential). Its inhibition can cause the cessation of the respiratory rhythm, while the use of agonists causes an increase in it.
When it comes to reducing the respiratory rate, the neurotransmitters that seem to act the most are GABA and glycine.
In addition to the above, there are other neurotransmitters that influence the respiratory rhythm through this structure. Although they do not participate directly in the genesis of the respiratory rhythm, they do modulate it. Examples of this are found in serotonin, adenosine triphosphate or ATP, substance P, somatostatin, norepinephrine, opioids and acetylcholine. That is why many substances and drugs cause an alteration of the respiratory rhythm.
One aspect to keep in mind is that emotions also have an important effect on the respiratory rate, due to the effect on this area of the secreted neurotransmitters. For example, in the case of experiencing nervousness or anxiety, an increase in the respiratory rate is observed, while in the face of hopelessness and depression it tends to slow down.
Effects of injury to this area
Although the preBötzinger complex is not the only element involved in respiratory control, it is currently considered the main element in charge of regulating it. Alterations in this area can cause consequences of different magnitude, such as respiratory increase or depression. And this can come from congenital injuries, trauma, cardiovascular accidents or administration of psychoactive substances. In extreme cases it can lead to the death of the patient.
It has been observed in the postmortem analysis of people with dementia with Lewy bodies or atrophy, a decrease in the population of neurons reactive to the previously mentioned neurokinin-1 is usually observed, which may explain the presence of respiratory disorders in these diseases.
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- García, L .; Rodríguez, O. and Rodríguez, OB (2011). Regulation of respiration: morphofunctional organization of its control system. University of Medical Sciences. Santiago de Cuba.
- Muñoz-Ortiz, J .; Muñoz-Ortiz, E .; López-Meraz, ML; Beltran-Parrazai, L. and Morgado-Valle, C. (2016). The pre-Bötzinger complex: generation and modulation of the respiratory rhythm. Elsevier. Spanish Society of Neurology.
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