Influence of Laryngeal Reflex on Phonation

Abstract

Eleven adult cats were anesthetized with intramuscular injection of Ketamine hydrochloride. Electrically induced vocalization was performed after Kanai's methode. (stimulating location APO, L4.5-5.5, H-3.5-6.0) The internal branch of the superior laryngeal nerve was cut and the peripheral stump was placed on a pair of silver recording electrodes. Then afferent discharges from laryngeal sensory receptors during electrically induced vocalization were recoded.
In this study, 16 single afferent discharges were obtained. They were classified into four groups. Discharge rate of the first group corresponded to the fundamental frequency change during evoked vocalization. Discharge rate of the second group showed augmentation during evoked vocalization but was not correlated with the fundamental frequency change. Discharge rate of the third group decreased during evoked vocalization. Receptors of the fouth group showed activities only at the initiation time of the evoked vocalization.
In 3 out of 7 successfully investigated cases, we observed that the pitch of evoked vocalization decreased after section of the internal branch of the superior laryngeal nerve. In the other cases, we observed hoarseness and an increase of the induced vocalization cycle.
These results suggest that central nerve system receives real time informations from the larynx during evoked vocalizatios and laryngeal sensory receptors play some role in the control mechanism of phonation.