2000 Volume 12 Issue 2 Pages 64-68
The intrinsic laryngeal muscles have particular characteristics functionally, histochemically and ultrastructurally compared with common skeletal muscles. In the present study, age-related morphological changes of the subneural apparatus (SNA) is assessed of the cricothyroid (CT), thyroarytenoid (TA) and posterior cricoarytenoid (PCA) muscles in rats using scanning electron microscopy.
The SNAs of these muscles were immature at 1 week postnatally showing single oval primary synaptic cleft and a small number of secondary synaptic clefts. At 4 weeks postnatally, structures of the SNAs of the CT and TA muscle became mature, while, those of the PCA muscle were delayed in maturation. In aged rats, the CT and TA muscles showed little age-related morphological change. However, the PCA muscle presented some changes including an increased number of depression-type primary synaptic clefts, multiple SNAs on muscle fiber, and thin muscle fiber containing immature SNA. The structure of the SNA was quantitatively analyzed by use of the following parameters, areas of primary and secondary synaptic clefts (APC and ASC, respectively) and length /width (L/W) ratio of the secondary synaptic clefts. APC was roughly constant througthout the tissue life. ASC and L/W ratio increased during the early postnatal period, while, it remained stable with aging. These findings suggest that age-related changes of the CT and TA muscles rarely occur, thereby contributing to their functional maintenance. However, in the PCA muscle, muscle fiber remodeling seems to occur more frequently than in the CT and TA muscles with aging.
