Electromyographic (EMG) responses of the intrinsic laryngeal muscle have been investigated to clarify reflexogenic laryngeal controls from a viewpoint of its functional significance during phonation.
Twenty-five adult cats were anesthetized with intraperitoneal injection of 4ml/kg of a mixture of 10% urethane and 1% alpha-chloralose. Either the internal branch of the superior laryngeal nerve (ISLN) or the recurrent laryngeal nerve (RLN) was carefully dissected and central end of the dissected nerve was electrically stimulated. EMG of the contra-lateral Thyro-Arytenoid muscle (TA muscle) to the stimulation was recorded using a hooked-wire electrode inserted through the laryngeal mucosa.
EMG of the TA muscle evoked by the stimulation of the ISLN were analized with respect to its latency and discharge pattern either in intact cat or inter-collicular brainstem transsected.
Together with the electrical stimulation of the RLN, vibratory stimuli were given mainly to the subglottic mucosa as conditioning stimuli. The vibratory frequency was changed from 50Hz to 400Hz stepwisely.
Following results were obtained.
1. EMG response of the contra-lateral TA muscle to the stimulation of the ISLN showed two different kinds of latency, approximately 8-10msec, and 40-60msec.
2. After inter-collicular brainstem transsection, evoked response of the latter disappeared. This result indicates that the ISLN-RLN reflex loop consisted of more than two routes, different in the number of synaptic junctions.
3. The vibratory stimuli given to the laryngeal mucosa had facilitatory effect on the reflexive EMG response evoked by the stimulation of the RLN.
4. This facilitatory effect of the vibratory stimuli disappeared after topical anesthesia of the laryngeal mucosa.
5. The facilitatory effect on the reflex responses was partially increased depending on the vibratory frequencies applied.
In conclusion, vibratory stimuli to the laryngeal mucosa reflexively modulate the activity of the intrinsic laryngeal muscles.
