Muscle function during feeding through infancy

Muscle function during feeding through infancy

Mayerl CJ;Tobin H;Chava A;Edmonds C;Gould FDH;Stricklen B;Bond L;German RZ

Faseb Journal

2020

2020-04

Infant mammalian feeding is a complex process that requires the integration of different behaviors and over twenty‐five muscles controlled by multiple cranial nerves. Despite extensive characterization of muscle activity during a feeding sequence, from suckling to swallowing, specific biomechanics of muscle function are unknown. The function of a muscle is determined by both when the muscle is active and the line of action of the muscle, as well as the change in length during activity. In mammals, there is potential for the line of action of the muscles involved in swallowing to change through ontogeny, as infants have a compressed oropharyngeal anatomy relative to adults. Additionally, while we understand when muscles are active during infant feeding, little has been done to understand whether those activity patterns correspond to concentric, eccentric, or isometric contractions. Here, we used contrast‐based microCT scanning coupled with electromyography (EMG) and fluoromicrometry to test the possibility that muscle function changes through infancy using our validated infant pig model. We collected anatomical data from pigs at infancy and just prior to weaning (21 days old), and isolated muscles of interest in Avizo. We collected EMG and fluoromicrometry data from five muscles involved in feeding (Geniohyoid, Digastric, Stylohyoid, Thyrohyoid, and Omohyoid) at the same ages. We found substantive changes in muscle anatomy through infancy and found extensive variation in muscle firing patterns and function within muscles. Some muscles (eg thyrohyoid) exhibited concentric contractions, whereas other muscles were eccentric (eg omohyoid). Still others exhibited multiple functions, and were eccentric during sucking EMG bursts, but isometric during swallowing EMG bursts (eg geniohyoid). Additionally, we found regional heterogeneity in muscle firing patterns in some muscles (eg stylohyoid), whereby electrodes placed in the middle of the muscle showed activity during swallows, but electrodes placed closer to the hyoid (more ventrally) recorded activity during sucking and swallowing. These results highlight the complexity of infant mammal feeding and demonstrate that muscle activity does not necessarily indicate muscle function. Instead, many muscles that are traditionally thought to function to pull the hyoid along their line of action may actually be functioning to stabilize the hyoid during swallowing. This suggests that control and coordination of the oropharyngeal structures is likely to be more important for successful feeding function than strength or the velocity of moving those structures.

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journalArticle

S1

34

0892-6638

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