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The respiratory centers (RCs) are located in the medulla oblongata and pons, which are parts of the brainstem. The RCs receive controlling signals of neural, chemical and hormonal nature and control the rate and depth of respiratory movements of the diaphragm and other respiratory muscles. Injury to these centers may lead to central respiratory failure, which requires mechanical ventilation and is usually associated with a poor prognosis.
In healthy individuals the presence of elevated carbon dioxide levels in the blood lowers its pH. Chemoreceptors found in carotid bodies and aortic bodies detect a decrease in blood pH and send this information to the RCs which then signal the respiratory muscles to breathe.
The respiratory centers are divided into four major groups, two in the medulla and two in the pons. The two groups in the medulla are the dorsal respiratory group and the ventral respiratory group. The two groups in the pons are the pneumotaxic center (also known as the pontine respiratory group), and the apneustic center.
Inspiratory center (Dorsal respiratory group)
- Location: Dorsal portion of medulla
- Nucleus: Nucleus tractus solitarius
Expiratory center (Ventral respiratory group)
- 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.
- Location: Pons (upper part)
- Nucleus: Nucleus parabrachialis
- Function: It controls both rate and pattern of breathing. Limit inspiration.
- Location: Pons (lower part)
- It discharges stimulatory impulse to the inspiratory center causing inspiration.
- It receives inhibitory impulse from pneumotaxic center and from stretch receptor of lung.
- It discharges inhibitory impulse to expiratory center.
Respiratory center depression
Depression of a respiratory center can be caused by:
- drugs (μ-opioids, sedatives, etc.)
- sudden cessation of blood circulation in brain
- severe brain trauma
- brain tumors
- damage of the brainstem
Respiratory center stimulation
Amphetamine stimulates the medullary respiratory centers, producing faster and deeper breaths. In a normal person at therapeutic doses, this effect is usually not noticeable, but when respiration is already compromised, it may be evident.