New Measurements of the Capacity and the Resistance of the Myelin Sheath and the Nodal Membrane of the Isolated Frog Nerve Fiber

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Abstract
The leakage of action current through the myelin sheath was recorded at the site of collision of two nerve impulses. By separating this leakage current into the capacitative and the ohmic components, the capacity and the parallel resistance of the myelin sheath were determined. For large myelinated nerve fibers (12 -15 [mu] in outside-diameter) of the bull frog, the capacity was found to be 1.6 [mu][mu]f/mm and the resistance to be 290 megohm-mm. The capacity and the resistance of a node of Ranvier treated with a Na-free Ringer were determined by using a similar collision technique. The capacity of the nodal membrane was found to be 1.5 [mu][mu]f and its resistance to be approximately 40 megohms. Various chemicals change the resistance of the nodal membrane, just as they do the resistance of the myelin sheath. The capacity of the nodal membrane, just as that of the myelin sheath, is not altered by chemicals. A hypertonic NaCl solution reduces the membrane resistance. A strong cocaine-Ringer solution increases it, but a weak cocaine-Ringer solution, which is still strong enough to abolish the response of a node completely, does not change the membrane resistance. Gradual removal of the myelin substance by saponine increases the capacity and decreases the resistance of the myelin sheath. Lowering of the temperature increases the membrane resistance. This temperature dependence is greater than that of the specific resistance of a frog Ringer.