Abstract
The purpose of the present investigation is to determine the roll of intrinsic and extrinsic laryngeal muscles in laryngeal closure reflex during deglutition. Two types of experimental investigations were performed:(1) observations of intralaryngeal movements during electrical stimulation of selected muscle (s), and (2) observations of the laryngeal closure during the swallowing caused by electrical stimulations of the superior laryngeal nerve in normal condition and when some selected muscle (s) were deleted. Thirty-eight mongrel dogs were used for the experimental animals. The closure of the larynx during swallowing were photographed on 16 mm movie films under a suspension laryngoscope and were investigated with frame by frame analysis.
On the basis of the results of the experiments, the following conclusions appear justified:
1. In the normal dogs, the laryngeal cavity is closed completely with a consistent time program during the swallowing.
2. When the bilateral recurrent laryngeal nerves are sectioned, the closure of the larynx is markedly disturbed. Even in this situation, however, a complete closure of the larynx still takes place, although the closed period is extremely short.
3. When the bilateral pharyngeal constrictor muscles are sectioned in addition to the previous condition, the closure of the larynx is markedly affected and there is no glottic closure at all.
4. After section of the bilateral inferior constrictor muscles, suprahyoid muscles and hypoglossal nerves respectively, laryngeal closure occurs in a similar way as to that in the control. No significant disturbances in laryngeal closure are found during the swallowing.
