In the present paper the ultrastructural similarities among the terminal portions of Pacinian corpuscles, the nodes of Ranvier, and the initial segments of primary sensory neurons are pointed out. Our conclusion is based on our observations of cat Pacinian corpuscles and other general knowledge of the node of Ranvier and the initial segment published elsewhere. The morpho-functional similarities of three principal excitable regions of the sensory nerve fibres (the initial segments, the node of Ranvier, and the terminal portions of sensory nerve formations) are illustrated by identical distribution of the enzymes which are associated with ionic transport (alkaline phosphatase, Mg(2+)-ATPase), and non-specific cholinesterase. Furthermore, the polyanionic material revealed by Alcian blue staining in three excitable sites of the sensory axon confirms the supposition that excitable axolemma cannot be considered in the isolation of its surroundings produced by Schwann cells.

Department of Anatomy Medical Faculty Masaryk University Brno Czech Republic