Nerve endings in rat carotid body.

The carotid body of the rat consists of "glomera" interspersed by blood vessels and nerve bundles. Each "glomus" consists of 2-12 Type I cells, incompletely invested by 1-3 Type II cells. Type I cells are characterised by the presence of numerous dense cored vesicles in their cytoplasm and may exhibit "synaptic" -like contacts with each other. Small efferent nerve endings make synaptic contact with one or more Type I cells. Large cup-shaped afferent nerve endings make multiple synaptic contacts of two kinds with one or more Type I cells. A second kind of efferent nerve ending is occasionally seen in synaptic contact with one of these afferent nerve endings. A model for the mode of operation of the glomus as a chemoreceptor is proposed.