Membrane resting and action potentials from single myelinated nerve fibers.

1.The development of the capillary microelectrode has been reviewed and the possibility that this technique can be used to obtain simultaneous measurements of the membrane resting and action potentials from single myelinated nerve fibers in situ is brought forward. 2. The electrical properties of the CME are discussed with respect to the distortion of changes in potential which it introduces. A suitable approximation is developed whereby this distortion can be corrected for mathematically. 3. The development of electronic equipment which performs the necessary operations on the action potential is described. It is this new method of correction which makes the use of this technique practicable. 4. Data on membrane resting and action potentials, relative thresholds, strength-duration relations, recovery of excitability and conduction velocity are presented for A fibers of frog sciatic nerve. 5. The average values of 17 pairs of data on resting and action potentials, selected on the basis of certain well justified assumptions, are resting potential 56 mv and action potential 73 mv. The average action potential is 30% greater than the average resting potential. The largest action potential recorded was 170 mv with a resting potential of 65 mv. The actual values are estimated as 60-70 nv for the resting potential and 100-120 mv for the action potential. 6. Two distinct action potential shapes, N and I, were distinguished and reasons given for believing that they were recorded in nodal and intermodal regions, respectively. 7. The relationship between rise time and conduction velocity established by previous workers has been confirmed. 8. The electronic correction of the action potential is shown to be valid by comparison with graphical reconstruction. 9. Records showing that conduction block occurs in a quantized manner are shown to be interpretable only in terms of the theory that conduction is salutatory in these nerves. 10. The mathematical description of the upike potential developed by Rosenblueth et al. was applied with only moderate success to membranal action potentials. 11. Strength-duration curves obtained on 12 different fibers were nearly identical in shape. One of the points on the curve is in marked disagreement with excitation theory. The time constant of excitation is 0.180 msec. 12. Excitabilitiy-time after recover curves were obtained in three instances. The absolutely refractory periods were 2-3 msec. 13. The relationship between conduction velocity and threshold established by previous workers was confirmed. 14. Reasons for believing that the records obtained were actually made transmembranally are given. 15. The future possibilities of further work along this line and ways of improving the present technique are discussed.