Closure of the Larynx During the Swallowing

Abstract

In spite of the clinical importance, there is little experimental informations on the influences of deletion of selected muscles upon the protective closure of the larynx during swallowing.
In this study, particular attention was paid to the roll of selected muscles in and around the larynx upon the laryngeal movements during the swallowing. Two different experimental procedures were adopted using mongrel dogs. In the first series of the experiments, laryngeal closure during the swallowing were photographed on 16mm movie films under a suspension laryngoscope. In the second series, electrical activity of several muscles in and around the larynx was recorded during the swallowing simultaneously with up and down movements of the entire larynx with a polygraph unit. Each recording was made while the the action of selected laryngeal muscles were deleted.
On the basis of the results of the experiments, the following conclusions appear justified:
1. In the normal dogs, each muscle is activated under a consistent time program during reflex 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 inferior 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 are at all.
4. Upward movement of the hyoid bone is performed mainly by the action of the suprahyoid muscles, particularly the geniohyoid muscle. The intrinsic and extrinsic muscles of the tongue also participate in the elevation of the hyoid bone.
5. The elevation of the larynx is chiefly performed by the action of the thyrohyoid muscle with co-operation of the suprahyoid muscles.