While neck muscles are crucial for stabilizing and mobilizing the head and cervical spine, their morphological and histological characteristics in healthy individuals remain under-researched. This doctoral thesis investigated the composition of the splenius capitis muscle in healthy younger and older men, as well as in men with type 2 diabetes. The investigation focused on myosin heavy chain expression, muscle fiber size, lipid content, and capillary network characteristics. Autopsy samples of the splenius capitis and vastus lateralis (a commonly studied muscle serving as a comparative control) were obtained from 13 younger healthy men, 12 older healthy men, and 25 obese older men with type 2 diabetes. Muscle fiber proportions and sizes, lipid content, and three-dimensional capillary network architecture were analyzed in both muscles. Comparisons between healthy men revealed similar capillary network density and fiber lipid content in younger and older individuals. However, older men exhibited a smaller proportion and size of fast-twitch type 2 fibers. In contrast to older healthy men, diabetic men demonstrated no differences in capillary network density, but displayed a higher proportion of type 2 fibers, larger type 1 fibers, and greater lipid content within type 1 fibers. These findings in the splenius capitis suggest a shift towards a faster muscle fiber phenotype in diabetic men. The consistent capillary network density, despite variations in fiber size and proportions across groups, suggests a dynamic adaptation that preserves blood supply irrespective of structural alterations in muscle fibers. This research provides the first comprehensive analysis of splenius capitis muscle composition in healthy younger and older men, as well as in men with type 2 diabetes. These findings establish a foundation for future investigations into the impact of pathological conditions on the splenius capitis muscle.
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