Light- and electron-microscopic investigations on human carotid bodies.

The functionally first of all considerable components of the carotid bodies are glomus cells and nerve fibres. The glomus cells form two groups. The chemoreceptor cells belong in one of these, the capsular cells in the other. The chemoreceptor cells are polygonal bodies. in their cytoplasm, organella are expressed. The cell nucleus is round, chromatin is homogeneous. Cells are characterized by the osmiophilic bodies. The capsular cells are long-shaped bodies with processes, they are associated with the chemoreceptor cells and sometimes lap over these, like veils. A number of the nerve fibres take place in Schwann's cells wrapped in a mesaxon membrane. The larger part, surrounds the round cell-nests consisting of chemoreceptor cells with a close-meshed network. From the network some fibres draw to the chemoreceptor cells and terminate on these in the form of boutons. Nerve endings form synapses with the chemoreceptor cells. Three forms of these have been found. One of these is the conventional synapsis, the other the saccular synapsis and the third one the parallel contact. Conventional synapses contain all the components identified in the neurons of the central nervous system. Saccular synapses are the magnified pictures of boutons. They consist of axolemma, axoplasm, synaptic vesicles, and mitochondria. In the parallel contacts, the axolemma and cytolemma touch each other. In the axoplasm, there are synaptic vesicles and mitochondria. Conventional synapses conduct peripherally, saccular synapses and parallel contacts centrally. On chemoreceptor cells, there are no neuronal marks, consequently, they are no interneurons. For reciprocal synapses the morphological bases are missing. The chemoreceptor cells are sensory cells.