The Respiratory Center: Neural Control of Breathing Rate and Depth

Anatomy

The respiratory centers are clusters of neurons in the brainstem (pons and medulla) that generate and modulate the respiratory rhythm.

Key Nuclei

Center	Location	Function
Dorsal Respiratory Group (DRG)	Medulla (nucleus of tractus solitarius)	Primary inspiratory drive; integrates peripheral chemoreceptor input
Ventral Respiratory Group (VRG)	Medulla (nucleus ambiguus, retrofacial)	Active expiration (recruited during exercise); contains pre-Bötzinger complex (rhythm generator)
Pneumotaxic Center	Upper pons (nucleus parabrachialis)	Limits inspiration → increases respiratory rate, decreases tidal volume
Apneustic Center	Lower pons	Prolongs inspiration (inhibited by pneumotaxic center)

Chemical Control

• Central chemoreceptors (medullary surface): Respond to CSF pH (driven by arterial CO₂). Primary drive for ventilation.
• Peripheral chemoreceptors (carotid/aortic bodies): Respond to low PaO₂ (<60 mmHg), high PaCO₂, low pH. Important in hypoxia and acidosis.

Mechanical Feedback

• Pulmonary stretch receptors (Hering-Breuer reflex): Inhibit inspiration at high lung volumes.
• J-receptors (juxtacapillary): Stimulate rapid shallow breathing in pulmonary edema.
• Muscle/joint proprioceptors: Increase ventilation with movement (exercise).

Clinical Relevance

Opioids depress the pre-Bötzinger complex → respiratory depression. Brainstem strokes cause apneustic or ataxic breathing. Chronic CO₂ retention (COPD) blunts central chemosensitivity, shifting drive to hypoxic drive.