Figure 4.

Major pontine and medullary regions involved in the cardiovascular and respiratory responses to peripheral chemoreflex activation. Aortic and carotid bodies and supra-medullary pathways are not shown. Observe that peripheral chemoreflex activation recruits several brainstem nuclei in series and in parallel in order to produce a patterned and integrated cardiorespiratory response to hypoxia, which is characterized by (1) bradycardia, represented here as a decrease in instantaneous heart rate; (2) sympathoexcitation, demonstrated here as increases in the amplitude of thoracic sympathetic nerve activity; (3) tachypnea, show as an increase in the frequency of phrenic nerve bursts; and (4) forced expiration, here seen as an increase in the activity of the abdominal muscles during the expiratory phase of the respiratory cycle. NTS, nucleus tractus solitarii; NA, nucleus ambiguous; RTN/pFRG, retrotrapezoid nucleus and the parafacial respiratory group; BötC, Bötzinger Complex; preBötC, pre-Bötzinger Complex; rVRG, rostral ventral respiratory group; cVRG, caudal ventral respiratory group; RVLM, rostral-ventrolateral medulla; CVLM, caudal-ventrolateral medulla.