Abstract
Swallowing is made up of a set of complex physiological movements resulting from a series of muscle contractions under precisely controlled neural innervation. Swallowing is thought to be immature immediately after birth. With physical development, swallowing movements become mature. The hypopharyngeal constrictor muscle, which plays an essential role in mature swallowing, consists of two different muscles having diverse functions: the thyropharyngeal muscle (TP), which drives the bolus into the esophagus, and the cricopharyngeal muscle (CP), the constrictor of the upper esophagus at rest. For this paper, the author investigated histochemically the differential pattern of the canine hypopharyngeal constrictor muscle, using the ATPase stain technique, in respect to functional development and the maturity of the TP and CP.
Compairing the proportion of muscle fiber types between two-week-old, two-month-old and adult dogs, the TP showed an earlier differentiation than the CP. As for the mean diameters of the type 1 and 2 fibers, the TP similarly differentiated earlier than the CP muscle.
To determine whether this differential pattern is specific to the hypopharyngeal constrictor muscle or not, the author observed the proportions of the constituent fibers and their diameters at 1, 2, 4, 6 and 9 weeks after birth between the TP, CP, extensor digitorum longus (EDL, type 2 fiber predominant in adult) and flexor digitorum superficialis (FDS, type 1 fiber predominant). The TP appeared to mature earlier than the EDL, while the CP seemed to differentiate later than the FDS.
These findings suggest that the differential pattern of the hypopharyngeal constrictor muscle may be specifically related to the maturity of swallowing movements after birth.
