Structure of the satellite cell sheath around the cell body, axon hillock, and initial segment of frog dorsal root ganglion cells.

The structure of the satellite cell sheath of frog dorsal root ganglion cells was studied in thin sections and freeze-fracture replicas. The sheath around the cell body is composed of thin satellite cell lamellae closely applied to the neuronal plasma membrane. At the axon hillock the sheath divides into outer and inner components separated by a broad space containing a distinctive extracellular matrix and occasional flattened satellite cell processes. The sheath around the initial segment is usually multilayered but less compact than that around the cell body, and in some places it exhibits node-like interruptions. Apart from occasional particle groupings characteristic of tight junctions and gap junctions, the satellite cells display homogeneously distributed intramembranous particles in both fracture faces in all regions of the sheath.