The act of swallowing at the laryngeal level is made up of two movements of the epiglottis:
The first which brings the epiglottis to be from a vertical position to a transverse one. This movement is created by the elevation of the larynx with the hyoid bone and thyroid cartilage approaching. The movement is passive, induced by the muscles that elevate the hyoid bone.
The second, which brings the epiglottis back from the transverse position to the initial vertical position (rest position), occurs in the second phase of swallowing and is probably related to the thyroepiglottic muscle.
Protection of the larynx during swallowing is essential to prevent aspiration.
The entry of the bolus into the airways during swallowing is prevented by 3 different mechanisms:
the obturation of the rima of the glottis
the closure of the laryngeal vestibule
the tilting of the epiglottis downwards to cover the laryngeal narrow
It is precisely the third component, that of 'tilting', that is activated by a sequence in two acts, in which at the end of the oral preparation of the bolus the larynx rises, the hyoid bone approaches the mandible and the distance between the hyoid and thyroid cartilage is reduced.
Synchronously with the elevation of the larynx, the epiglottis tilts by approximately 90° from its vertical rest position, moving into a transverse position with its free edge closed on the posterior pharyngeal wall (this phase corresponds to the first epiglottic movement).
Simultaneously with the elevation of the larynx, the bolus enters the pharynx where a peristaltic contraction begins.
At this point the epiglottis tilts further downwards, unfolding its free edge into the esophageal strait (this is the second epiglottic movement).
During this last phase the epiglottis changes its shape, becoming a caudal concavity with its lower surface pressed against the aryepiglottic region.
The epiglottis specifically is a cartilage suspended from adjacent structures by fibroelastic elements.
The petiole is attached via the thyroepiglottic ligament to the superior posterior aspect of the isthmus of the thyroid cartilage.
The anterior surface of the epiglottis is connected by the hyoepiglottic ligament to the hyoid bone.
Laterally it is suspended from the quadrangular membrane. The upper border of this membrane is the aryepiglottic layer. Its inferior margin is composed of the vestibular ligament, while the posterior margin is the arytenoid cartilage.
It is this suspension of the epiglottis that causes the movements of the thyroid cartilage and hyoid bone to be promptly transmitted to the epiglottis.
Furthermore, a change in the mutual position of the thyroid cartilage and hyoid bone is necessarily followed by a change in tension of the epiglottis cartilage and its suspension system, followed in turn by a change in position. Bringing these two structures closer together allows the epiglottis to tilt downwards into a transverse position, while their subsequent removal brings the epiglottis back to its vertical rest position.
The first movement of the epiglottis is passive, induced by the muscles that elevate the hyoid bone, and which bring the thyroid cartilage closer to the hyoid bone. These muscles are: stylohyoid, digastric, mylohyoid, geniusoid, thyrohyoid. The epiglottis is fixed bilaterally by the pharyngoepiglottic folds and when tilted into a transverse position this fold is the rotation pivot.
The three muscles, stylopharyngeal, aryepiglottic and thyroepiglottic, insert on the epiglottis in such a way that their contraction modifies their position.
The stylopharyngeal muscle emerges from the styloid process and passes in an antero-inferior direction to the process itself, between the superior and middle pharyngeal constrictors up to the epiglottis and the thyroid cartilage. This fan-shaped muscle intersects with the palatopharyngeal muscle.
The aryepiglottic muscle instead passes under the aryepiglottic fold between the arytenoid region and the lateral margin of the epiglottis.
The thyroepiglottic finally emerges from the posterior surface of the thyroid cartilage in a posterior direction. It inserts at the lateral margin of the epiglottis and the aryepiglottic layer.
When the epiglottis, from an elevation of the larynx and approximation of the thyroid cartilage to the hyoid bone, has reached a transverse position, the situation changes. The muscles that insert on the epiglottis probably responsible for the subsequent movement are the aryepiglottic muscle and the thyroepiglottic muscle. The stylopharyngeus can be excluded because due to its position, it can elevate the epiglottis but cannot pull it down onto the arytenoid region. It is likely, however, that the aryepiglottic muscle can pull the epiglottis down towards the arytenoid region, but never as low as in the esophageal strait. It is the thyroepiglottic muscle that inserts onto the epiglottis which however has another action on the epiglottis when it is in a transverse position. With the epiglottis in that position, its contraction pulls the free portion down towards the arytenoid region with its apex in the esophageal narrow. In maximal tension the position of the epiglottis is then modified from convex at the bottom to convex at the top, subsequently bringing it back to verticality. With the epiglottis in this position a contraction of the aryepiglottic hardens the laryngeal narrow.
A careful osteopathic evaluation of the cranio-cervical-laryngeal district is specifically aimed at monitoring the laryngeal and extra-laryngeal biomechanical-functional state in order to be able to identify and correct those structures that potentially create alterations in voluntary and involuntary mobility during the act swallowing.