Measurement of the Action-Potentials in the Peripheral Nerves of Man Without Anesthetic

Abstract

Our method to secure records of nerve currents in man is to insert one or both electrodes directly into a peripheral nerve. Two types of electrodes are used: (1) A fine wire of platinum-indium is inserted into the ulnar nerve while a second wire is inserted under the skin at the point of the elbow. The second wire is the so-called indifferent electrode. (2) The tip of a hypodermic needle containing 2 very fine and well-insulated wires, the electrodes, is inserted into the ulnar nerve. The needle itself is connected to ground, while the electrodes are connected with the amplifier input. Possible advantages of this type of electrode over the well-known form of Adrian are under investigation. Electrodes described under (2) are particularly suitable for measuring action-potentials from a limited area of nerve tissue immediately surrounding the electrodes.

Measurements are made with apparatus previously described, 1 including an amplifying equipment and string galvanometer so that if one microvolt at 60 cycles is impressed upon the input terminals of the amplifier a fairly steady deflection of the string of about 2.4 cm. is obtained. At this setting, if a short-circuiting line is placed across the input terminals, the string shows irregular excursions generally not exceeding 0.6 or 0.7 cm.

Whether the electrode or electrodes actually are in the nerve can be determined as follows: (1) As the needle penetrates the nerve, the subject reports a sudden pang in the ulnar portion of the palm and in the ulnar 2 fingers, sometimes including the middle finger. (2) Leads from the electrodes are disconnected from the amplifier and connected into a circuit containing a dry cell and a rheostat, so that a slight stimulating current can be sent through the tissues between the points of the electrodes.