ACTION POTENTIALS FROM SINGLE MUSCLE FIBERS

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Abstract
The action potentials of single muscle fibers in the retrolingual membrane and in the sartorius muscle of the greenfrog were recorded on the cathode ray oscillograph, with an amplitude of 15 mm. at a sensitivity of 60mm./mv. A technique is described for such recording with microelectrodes (7 to Kfyt) in which the tissue and electrodes are arranged as a Wheat-stone bridge to obviate distortion of the record by the electrical stimulus employed to excite. A conducted action potential is always accompanied by a conducted contraction, but below threshold for this, a localized shortening takes place at and near the stimulating cathode which is not accompanied, even locally, by an action potential. It is concluded that this localized shortening is of the character of a contracture, and probably represents the direct response of the muscle substance to passage of current in the sense of the well-known idiopathic galvanic contracture. Its spread to some distance (1/2 mm.) from the cathode is probably due to the spread through the tissue of the current that stimulates. As far as visual observation may detect, such con-tractures may be as short as normal twitches when currents of short duration are employed to excite them.

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