Medullary Respiratory Neurons

The respiratory neurons in the medulla seem to be aggregated into two groups (Fig. 1). One collection, the ventral respiratory group (VRG), forms a longitudinal column of neurons in the ventrolateral part of the medulla. It extends rostrally from the upper border of the spinal cord almost to the bulbopontine boundary. The other group, the dorsal respiratory group (DRG), is more circumscribed anatomically. It is located in a more medial and dorsal part of the medulla in the region of the ventrolateral nucleus of the tractus solitarius (NTS) and extends from the obex about 2.5 mm rostrally.

FIG. 1. Schematic depicting the organization of medullary respiratory neurons in the dorsal and ventral respiratory groups (DRG and VRG, respectively). Structures on one side only are shown. Axons from inspiratory bulbospinal neurons in the nucleus tractus solitarius (NTS) and the nucleus para-ambigualis (NPA) decussate rostral to the obex and extens caudally in the contralateral cord. Axons from expiratory bulbospinal neurons in the nucleus retroambigualis (NRA) decussate caudal to the obex. Bötz = Bötzinger complex in the nucleus retrofacialis; NA = nucleus ambigualis.

The nuclei of the solitary tract appear to function as relay stations for important respiratory and cardiovascular information. Afferents from pulmonary stretch receptors and carotid chemoreceptors and baroreceptors appear to synapse for the first time in the brain at this location.