Anatomical and physiological variation of the hyoid musculature during swallowing in infant pigs

Abstract

The function of a muscle is impacted by its line of action, activity timing and contractile characteristics when active, all of which have the potential to vary within a behavior. One function of the hyoid musculature is to move the hyoid bone during swallowing, yet we have little insight into how their lines of action and contractile characteristics might change during a swallow. We used an infant pig model to quantify the contractile characteristics of four hyoid muscles during a swallow using synchronized electromyography, fluoromicrometry and high-speed biplanar videofluoroscopy. We also estimated muscle line of action during a swallow using contrast-enhanced CT-scanned muscles animated to move with the hyoid bone and found that as the hyoid elevated, the line of action of the muscles attached to it became greater in depression. We also found that muscles acted eccentrically and concentrically, which was correlated with hyoid movement. This work contributes to our understanding of how the musculature powering feeding functions during swallowing.

Keywords: Biomechanics; DiceCT; Feeding; Fluoromicrometry; Muscle.

Fig. 1.

Muscles and their vectors at rest, and when the hyoid bone is elevated to its peak position. Lateral view of muscles of interest (A,C) at rest and (B,D) following mean hyoid elevation/retraction during a swallow. Top: skull with muscles; bottom: skull with muscle vectors. Green, geniohyoid; yellow, stylohyoid; red, omohyoid; pink, thyrohyoid.

Fig. 2.

Mean hyoid movements in dorsoventral and anteroposterior directions (lines)±standard deviation (shaded areas) for four pigs (different symbols). The hyoid moves primarily dorsoventrally and begins elevating prior to the onset of the swallow as identified by X-ray video (0,0 on the plot). It makes a quick turn following maximal elevation and has not reached its resting point by the time the epiglottis has finished its movement during the swallow. Darker colors indicate the beginning of the swallow, lighter colors indicate the end. Blue points, pig 1; orange points, pig 2; green points, pig 3; purple points, pig 4.

Fig. 3.

Muscle length changes during activity through a swallow are correlated with hyoid translations. Muscle length changes during EMG activity for the (A) geniohyoid, (B) stylohyoid, (C) thyrohyoid and (D) omohyoid, as well as hyoid movements in (E) anteroposterior and (F) dorsoventral movements, with time (s) on the x-axis. Increasing values with time in E indicate hyoid anterior movement, and increasing values with time in F indicate hyoid elevation. AP, anteroposterior; DV, dorsoventral; IMD, intermarker distance.