Abstract
The aim of this study is to investigate the chronological changes in the vocalis muscle histologically. The materials were excised human larynges at necropsy which were preserved in ten percent formalin solution. In order to select specimens without abnormal anatomical changes, the specimens from with otolaryngological diseases, hematological problems and severe metabolic disorders were excluded. Cross-sections with exact right angle against the longitudinal direction were resected at the midportion of the vocalis muscle, and the sections were embedded in paraffin, cut and stained with hematoxylin-eosin, Sudan-III and Sudan-black-B. One hundred and seventy-five specimens, eighty-nine males and eighty-six females, were measured in the cross-sectional area, the number of muscle fibers and the rate of lipofuscin deposition. The age ranged between fetus and eighty-five years. Twenty-five specimens which retained the muscular structure well were measured in the number and the diameter of red and white muscle fibers.
The cross-sectional areas of vocalis muscle were increased by fourth decade and then de-creased with aging in males, but there was no significant changes in females. While the total numbers of muscle fibers and the numbers of white muscle fibers were significantly reduced as the age advances, the red muscle fibers did not show significant changes in number. In the first decade, both red and white muscle fibers did not show apparent differences in fiber diameter, on the other hand, after the second decade there appeared a tendency that the diameter of white muscle fibers became greater. The population of muscle fibers with longer diameter increased with age. This tendency was more noticeable in white muscle fibers. Lipofuscin pigment, one of the substances which appears and deposits in some organs as the age advances, deposited in vocalis muscle fibers as well, and the rate of accumulation was significantly increased according with aging.
