Ultrastructural observations on nodes of Ranvier from isolated single frog peripheral nerve fibres

A preparative procedure is described by which well-preserved nodes of Ranvier from isolated frog peripheral nerve fibres may be obtained. The following steps are crucial: careful and gentle dissection and isolation of a single nerve fibre, mounting in a chamber limiting lateral movements of the fibre during the fluid exchange, simultaneous glutaraldehyde-OsO4 fixation and embedding in the same chamber used for fixation. Serial sectioning of individual nodes from both motor and sensory fibres made it possible to reconstitute three-dimensional models of several nodes and to study their morphology extensively. In addition to well-known ultrastructural features of the nodal and paranodal architecture, evaginations of a nodal membrane containing mitochondria and outpouchings of the paranodal axoplasm containing vesicles are described.