Respiratory center
To simplify matters , several different groups of central neurons are functionally combined as the respiratory center , which are mainly located in the elongated medulla ( medulla oblongata ) and together unconsciously regulate the rhythmic alternation of inhalation and exhalation .
Nodus vitalis or life node are earlier names for the not sharply delimited association of respiratory nerve cells in the lower brain stem.
Respiratory neuron groups
Breathing is controlled centrally in the interplay of various interconnected groups of neurons. Some also inhibit each other mutually, so that the alternating activity of inspiratory or expiratory neurons leads to the alternating activity of respiratory muscles, for the phase of inhalation or that of exhalation. This is because the mutually connected neurons (groups) also emit fiber strands that descend in the spinal cord and influence those motor neurons in the cervical and thoracic marrow that innervate the various respiratory muscles.
Most of these nerve cells are embedded in the reticular formation of the brain stem , sometimes in spatially delimitable core areas. A distinction is made in the medullary brain between a dorsal respiratory group (DRG) in the area of the nucleus tractus solitarii with (primary) inspiratory neurons and a ventral respiratory group (VRG) in the vicinity of the nucleus ambiguus with expiratory and (secondary) inspiratory neurons. In addition to these, there are other respiratory neurons in the elongated medulla (caudal to the exit of the ninth cranial nerve glossopharyngeal nerve ), as well as expiratory neurons in the two upper spinal cord segments (C1 and C2 of the cervical cord).
Morphologically, the individual areas are often not clearly demarcated, they rather represent functional units. Some of the nerve cells promote inhalation (inspiratory), some encourage exhalation (expiratory), another the pause after inhalation (post-inspiratory). It is their mutual interaction that generates the rhythm of breathing.
function
The task of the respiratory center is to ensure regular, orderly inhalation and exhalation and to adapt the breathing frequency and depth to the current needs of the organism.
Although breathing is a rhythmic process, there are no nerve cells in the respiratory center that are capable of creating an autonomous rhythm. Instead, the inspiratory neurons are first activated by afferents from the reticular formation, which take care of inhalation via efferents to the inspiratory respiratory muscles . At the same time, the expiratory neurons are inhibited so that the expiratory respiratory muscles are not activated at the same time via their efferents.
The activation of the inspiratory cells is then reduced and the expiratory cells are increasingly activated via a mechanism that has not yet been conclusively clarified, in which afferents from stretch receptors in the lungs are probably also involved. In resting breathing, there is initially a post-inspiration phase in which the respiratory muscles are inactive and exhalation takes place through passive restoring forces of the filled lungs and the thorax. When breathing is deepened, the expiratory muscles are actively exhaled via the expiratory neurons.
The cells of the respiratory center that generate the rhythm are also known as the pre-Bötzinger complex . Another special feature are chemosensitive nerve cells, the so-called central chemoreceptors , which react to a drop in the liquor pH value caused by an increase in the carbon dioxide concentration in the blood.
Nervous and hormonal adaptation of breathing activity
One form of breathing adjustment is the so-called Hering-Breuer reflex , in which afferents from stretch receptors in the lungs prevent excessive stretching. A similar reflex is the head reflex : If the lung volume decreases too much , the irritant receptors in the bronchial tree become active and activate the inspiratory neurons in the respiratory center.
The simplest mechanism for increasing breathing under load is the nerve activation of the respiratory drive in the respiratory center through stimulation from the cerebral cortex , the limbic system and the hypothalamus , i.e. from centers of the central nervous system that become active when the load is applied. Activation can also take place via the periphery , namely via proprioceptors in the muscles and via pain receptors . The respiratory drive is activated hormonally by adrenaline , thyroid hormones and steroid hormones . An activation of the pressoreceptors has an inhibitory effect on breathing .
Control of breathing via chemoreceptors
The chemoreceptors , which provide information about the partial pressures of oxygen and carbon dioxide as well as the pH value of the blood, represent an important affinity to the respiratory center . The strongest respiratory drive is provided by the increase in the blood content of carbon dioxide, weaker drive effects have a drop in the oxygen content and a drop in the pH value.
Pathological conditions of the respiratory center
In the event of disturbances or damage to the respiratory center and thus the central respiratory regulation, e.g. through poisoning or strokes , pathological forms of breathing can occur.
history
The breathing center was discovered in 1811 by Julien Jean Legallois (1770–1840).
Individual evidence
- ↑ Martin Trepel: Neuroanatomy. Elsevier, Munich 2012, ISBN 978-3-437-41299-8 , p. 145.
- ↑ a b c Speckmann u. a .: Physiology. Elsevier, Munich 2008. ISBN 978-3-437-41318-6 , p. 470 ff.
- ↑ a b c d Ch. Fahlke u. a .: Pocket Atlas of Physiology. Elsevier, Munich 2008, ISBN 978-3-437-41917-1 , p. 258 ff.
- ↑ Legallois, Julien Jean César. Retrieved February 1, 2014 .
