Granule-containing cells in the human superior cervical ganglion.

The fine structure of granule-containing cells in the human superior cervical ganglion is described. These cells are larger than the typical SIF cells in mammals and exhibit green-yellow fluorescence. They are characterized by numerous granular vesicles (80-140 nm in diameter) in the cytoplasm, but have many features in common with ordinary ganglion cells. They emit several long processes which form bundles together with ordinary nerve fibers. No synapses are found where the cells are presynaptic, although a few synapses are observed there where nerves are prosynaptic on the perikarya and processes of the cells. No close topographical relations are seen between the cells and blood vessels. It is suggested that the granule-containing cells are a special type of postganglionic aminergic neurons.