Figure 5

Distribution of extracellular potential (Ve) in the finite element model and corresponding changes in membrane potential (Vm) in the nerve fiber model. An example of both an Aβ fiber ( A-B ) and an Aδ fiber ( D-E ) are depicted. B and D are zoomed versions of A and D, respectively. The colored circles in A , B , D , E indicate the nodes of Ranvier in the models, and the colors indicate Vm. The stimulation current used to calculate Ve and Vm was 1 mA. Panels C and F illustrate the locations of the nodes of Ranvier (black dots) that were activated in the models for Aβ and Aδ fibers, respectively. In C it can be seen that most Aβ fibers are activated at nodes which lie inside the dermis. The activation of Aδ fibers ( F ) occurred in the plexus which is located at a random depth within the most superficial 100 μm of the dermis. SC = stratum corneum, Epi = vital epidermis, Der = dermis. The electrode diameter is 9.1 mm, and r = 0 indicates the vertical symmetry axis in the model. The horizontal black lines indicate the boundaries between the different tissue layers. The color scale for Ve was truncated to clarify the potentials in the vital epidermis and dermis. The model geometries were taken for site 2, the lateral arch (Table 1). Note that the aspect ratios in B and E are not maintained to improve visualization.