Site of termination of primary afferents from the carotid body chemoreceptors.

The precise site of termination of primary afferents from the carotid chemoreceptors, has not been revealed as yet by anatomical or physiological studies. Identified units in the dorsal and ventral respiratory groups in the medulla can be evoked by chemoreceptor stimulation during inspiration, and inhibited by stimulation during expiration. Thus chemoreceptor input appears to be gated by an unidentified population of respiratory units before it reaches the recognized populations. For this as well as other reasons, we propose that chemoreceptor fibers terminate on a population of small interneurons that are the pattern generators for respiratory rhythmicity. At least two paired pattern generators exist, one pair associated with the dorsal respiratory group, and a second pair associated with the ventral respiratory group.