Studies of Action Currents in Laryngeal Nerves

In order to increase the information about the neurophysiological mechanism of phonation, action currents were recorded from the inferior and superior laryngeal nerves during voice production in dogs. The whining or barking sound produced when the animal was just coming out of ether anesthesia was picked up by a condensor-microphone and amplified by a one-stage amplifier. Simultaneously with the voice the action currents appearing in the inferior and superior laryngeal nerves were picked up by platinum electrodes (in some experiments as a check-up by non-polarizable electrodes) and amplified by a 3-stage resistance coupled amplifier. The recording of both the voice and the action currents was done by means of a 3-element Westinghouse oscillograph.

The inferior laryngeal nerve was exposed just below the thyroid cartilage and the superior laryngeal nerve a few millimeters towards the entrance into the crico-thyroid membrane.

The records show that when no voice is produced the action current line is practically at rest. During voice production the action current line of the inferior laryngeal nerve shows regular oscillations having the same frequency as the voice line. The frequency of these action current oscillations changes with the pitch of the voice. In order to exclude any influence of a non-physiological source the experiment was frequently repeated with different forms of electrodes and after removing the amplifier completely from the operating room. Furthermore, if one electrode was removed from the nerve and placed upon nearby muscle tissue the regular frequencies disappeared.

In order to determine the direction in which the potential changes were traveling, the inferior laryngeal nerve was transsected and records taken from both the central and the peripheral end. Those from the central end still presented regular oscillations of a frequency equalling the pitch of the recorded voice sound.