Respiratory center

Respiratory center
Respiratory groups in the respiratory center and their influence
Identifiers
MeSH D012125
Anatomical terminology

The respiratory center is located in the medulla oblongata and pons, in the brainstem. The respiratory center is made up of three major respiratory groups of neurons, two in the medulla and one in the pons. In the medulla they are the dorsal respiratory group, and the ventral respiratory group. In the pons, the pontine respiratory group includes two areas known as the pneumotaxic centre and the apneustic centre.

The respiratory centre is responsible for generating and maintaining the rhythm of respiration, and also of adjusting this in homeostatic response to physiological changes. The respiratory center receives input from chemoreceptors, mechanoreceptors, the cerebral cortex, and the hypothalamus in order to regulate the rate and depth of breathing. Input is stimulated by altered levels of oxygen, carbon dioxide, and pH, by hormonal changes relating to stress, and anxiety from the hypothalamus, and also by signals from the cerebral cortex to give a conscious control of respiration.

Injury to respiratory groups can cause various breathing disorders that may require mechanical ventilation, and is usually associated with a poor prognosis.

Respiratory groups

The respiratory centre is divided into three major groups, two in the medulla and one in the pons. The two groups in the medulla are the dorsal respiratory group and the ventral respiratory group. In the pons, the pontine respiratory group is made up of two areas – the pneumotaxic centre and the apneustic centre. The dorsal and ventral medullary groups control the basic rhythm of respiration.[1][2]

Dorsal respiratory group

In the medulla, the dorsal respiratory group makes up the inhalation area of respiratory control.

Ventral respiratory group

In the medulla, the ventral respiratory group make up the exhalation area of respiratory control.

  • Location: Antero-lateral part of medulla, about 5 mm anterior and lateral to dorsal respiratory group
  • Nucleus: Nucleus ambiguus and nucleus retro ambiguus.
  • Function: It generally causes expiration but can cause either expiration or inspiration depending upon which neuron in the group is stimulated. It sends inhibitory impulse to the apneustic center.

Pontine respiratory group

In the pons, the pontine respiratory group includes the pneumotaxic and apneustic centers. These have connections between them, and from both to the solitary nucleus.[3]

Pneumotaxic center

The pneumotaxic center is located in the upper part of the pons. Its nuclei are the subparabrachial nucleus and the medial parabrachial nucleus.[4] The pneumotaxic center controls both the rate and the pattern of breathing. The pneumotaxic center is considered an antagonist to the apneustic center, (which produces abnormal breathing during inhalation) cyclically inhibiting inhalation. The pneumotaxic center is responsible for limiting inspiration, providing an inspiratory off-switch (IOS).[5] It limits the burst of action potentials in the phrenic nerve, effectively decreasing the tidal volume and regulating the respiratory rate. Absence of the center results in an increase in depth of respiration and a decrease in respiratory rate.

The pneumotaxic center regulates the amount of air that can be taken into the body in each breath. The dorsal respiratory group has rhythmic bursts of activity that are constant in duration and interval.[6] When a faster rate of breathing is needed the pneumotaxic center signals the dorsal respiratory group to speed up. When longer breaths are needed the bursts of activity are elongated. All the information that the body uses to help respiration happens in the pneumotaxic center. If this was damaged or in any way harmed it would make breathing almost impossible.

One study on this subject was on anesthetized paralyzed cats before and after bilateral vagotomy. Ventilation was monitored in awake and anesthetized cats breathing air or CO2. Ventilation was monitored both before and after lesions to the pneumotaxic center region and after subsequent bilateral vagotomy. Cats with pontine lesions had a prolonged inhalation duration.[7] In cats, after anaesthesia and bivagotomy, pontine transection has been described as evoking a long sustained inspiratory discharges interrupted by short expiratory pauses. In rats on the other hand, after anaesthesia, bivagotomy and pontine transection, this breathing pattern was not observed, either in vivo or in vitro. These results suggest interspecies differences between rat and cat in the pontine influences on the medullary respiratory center.[8]

Apneustic center

The apneustic center of the lower pons appears to promote inhalation by a constant stimulation of the neurons in the medulla oblongata. The apneustic center sends signals to the dorsal group in the medulla to delay the 'switch off', the inspiratory off switch (IOS) signal of the inspiratory ramp provided by the pneumotaxic centre. It controls the intensity of breathing, giving positive impulses to the neurons involved with inhalation. The apneustic center is inhibited by pulmonary stretch receptors and also by the pneumotaxic center. It also discharges an inhibitory impulse to the pneumotaxic center.

Respiratory rhythm

Breathing is the repetitive process of bringing air into the lungs and taking waste products out. The oxygen brought in from the air is a constant, on-going need of an organism to maintain life. This need is still there during sleep so that the functioning of this process has to be automatic and be part of the autonomic nervous system. The in-breath is followed by the out-breath, giving the respiratory cycle of inhalation and exhalation. The number of cycles per minute is the respiratory rate. The respiratory rate is set in the respiratory center by the dorsal respiratory group, in the medulla, and these neurons are mostly concentrated in the solitary nucleus that extends the length of the medulla.[9]

The basic rhythm of respiration is that of quiet, restful breathing known as eupnea. Quiet breathing only requires the activity of the dorsal group which activates the diaphragm, and the external intercostal muscles. Exhalation is passive and relies on the elastic recoil of the lungs. When the metabolic need for oxygen increases, inspiration becomes more forceful and the neurons in the ventral group are activated to bring about forceful exhalation.[10]

Clinical significance

Depression of the respiratory centre can be caused by: brain trauma, brain damage, a brain tumour, or ischemia. A depression can also be caused by drugs including opioids, and sedatives.

The respiratory centre can be stimulated by amphetamine, to produce faster and deeper breaths.[11] Normally at therapeutic doses, this effect is not noticeable, but may be evident when respiration is already compromised.[11]

See also

References

  1. ↑ Tortora, Gerard (2008). Principles of anatomy and physiology (12. ed.). Hoboken, N.J.: Wiley. p. 905. ISBN 978-0470-23347-4.
  2. ↑ Pocock, Gillian; Richards, Christopher D. (2006). Human physiology : the basis of medicine (3rd ed.). Oxford: Oxford University Press. p. 332. ISBN 978-0-19-856878-0.
  3. ↑ Song, G; Poon, CS (15 November 2004). "Functional and structural models of pontine modulation of mechanoreceptor and chemoreceptor reflexes". Respiratory physiology & neurobiology. 143 (2–3): 281–92. doi:10.1016/j.resp.2004.05.009. PMID 15519561.
  4. ↑ Song, Gang; Yu, Yunguo; Poon, Chi-Sang (2006). "Cytoarchitecture of Pneumotaxic Integration of Respiratory and Nonrespiratory Information in the Rat". Journal of Neuroscience. 26 (1): 300–10. doi:10.1523/JNEUROSCI.3029-05.2006. PMID 16399700.
  5. ↑ Dutschmann, M; Dick, TE (October 2012). "Pontine mechanisms of respiratory control". Comprehensive Physiology. 2 (4): 2443–69. doi:10.1002/cphy.c100015. PMC 4422496. PMID 23720253.
  6. ↑ Dutschmann, Mathias (2011). Comprehensive Physiology. [Bethesda, Md.]: John Wiley and Sons. ISBN 978-0-470-65071-4.
  7. ↑ Gautier, H; Bertrand, F (1975). "Respiratory effects of pneumotaxic center lesions and subsequent vagotomy in chronic cats". Respiration Physiology. 23 (1): 71–85. doi:10.1016/0034-5687(75)90073-0. PMID 1129551.
  8. ↑ Monteau, R.; Errchidi, S.; Gauthier, P.; Hilaire, G.; Rega, P. (1989). "Pneumotaxic centre and apneustic breathing: Interspecies differences between rat and cat". Neuroscience Letters. 99 (3): 311–6. doi:10.1016/0304-3940(89)90465-5. PMID 2725956.
  9. ↑ Hall, John (2011). Guyton and Hall textbook of medical physiology (12th ed.). Philadelphia, Pa.: Saunders/Elsevier. pp. 505–510. ISBN 978-1-4160-4574-8.
  10. ↑ Derrickson, Bryan (2008). Principles of anatomy and physiology (12th ed.). Hoboken, N.J.: John Wiley. pp. 905–909. ISBN 978-0470-39234-8.
  11. 1 2 Westfall DP, Westfall TC (2010). "Miscellaneous Sympathomimetic Agonists". In Brunton LL, Chabner BA, Knollmann BC. Goodman & Gilman's Pharmacological Basis of Therapeutics (12th ed.). New York, USA: McGraw-Hill. ISBN 9780071624428.

Further reading

  • Levitzky, Michael G. (2002). Pulmonary Physiology (6th ed.). McGraw-Hill Professional. pp. 193–4. ISBN 0-07-138765-X.
  • Costanzo, Linda S. (2006). Physiology (3rd ed.). Philadelphia, PA: Elsevier. p. 224. ISBN 978-1-4160-2320-3.
  • Shannon, Roger; Baekey, David M.; Morris, Kendall F.; Nuding, Sarah C.; Segers, Lauren S.; Lindsey, Bruce G. (2004). "Pontine respiratory group neuron discharge is altered during fictive cough in the decerebrate cat". Respiratory Physiology & Neurobiology. 142 (1): 43–54. doi:10.1016/j.resp.2004.05.002. PMID 15351303.
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