Normal human muscle is composed of many individual muscle fibers bundled together by layers of connective tissue that are arranged in a nesting-doll like fashion. The inner most structure, the single muscle fiber, is covered by a thin layer of primarily reticular fibers called the endomysium. The endomysium is quite inconspicuous and muscle fibers appear to be in direct contact with each other. The finest capillaries, nerve twigs and lymphatic capillaries are found within the endomysium. Groups of muscle fibers are bound together by the thicker perimysium, forming structures called fascicles. Capillaries, nerve fibers and lymphatic vessels also track in the perimyseum. Bundles of fascicles are encased within the dense irregular connective tissue of the epimysium. These connective tissue layers provide mechanical protection for the muscle fibers and increase the tensile strength of the muscle. The layers are continuous with the tendon, which provides attachment to bone. Individual muscle fibers are syncytia, formed by embryonic fusion of many myoblasts or later, myosatellite cells. Each muscle fiber contains many nuclei, peripherally positioned immediately adjacent to the sarcolemmal membrane. In healthy muscle only 3-5 percent of fibers contain nuclei that are located internally, within the cell, but many disease processes lead to internal nuclei. Each nucleus provides a segment of the cell with needed translated protein products.

peter

2008-02-20T12:04:00Z

HP:0011806, HP:0003706

human_phenotype

HP:0004303