Fig. 3-27. Saltatory conduction in myelinated axons.  A. Longitudinal section through a small myelinated axon in the peripheral nervous system (above dashed line) and in the central nervous system (below dashed line). Note difference in structure of nodal regions. (Landon and Hall, The myelinated nerve fibre, in Landon, The Peripheral Nerve. London: Chapman and Hall, 1976).  B. Equivalent circuit for a region of internode, showing how membrane resistances, R_m, and capacitances, C_m are arranged in series, making resistance very high, capacitance low in the internode.  C. Equivalent circuit for two nodes and and intervening internode with values of membrane resistance, membrane capacitance, and internal longitudinal resistance inserted (Aidley, The Physiology of Excitable Cells. Cambridge: Cambridge Univ. Press, 1971).