perimysial

Perimysial refers to the perimysium, the connective tissue sheath that surrounds a bundle of skeletal muscle fibers, known as a fascicle. The perimysium lies between the endomysium, which ensheathes individual muscle fibers, and the outer epimysium that encloses the whole muscle. It is composed mainly of dense irregular connective tissue rich in collagen fibers (types I and III) with some elastic fibers, and it contains blood vessels, nerves, and lymphatics supplying the fascicles.

The perimysial network provides mechanical support for the fascicles and forms septa that organize muscle into functional compartments. It serves as a conduit for the vascular and neural elements that service the muscle fibers within each fascicle and contributes to the overall distribution of force during contraction. The perimysium also participates in the transmission of force from the contractile fibers to the tendons, interacting with the endomysial and epimysial layers to coordinate muscle mechanics.

Variations in thickness and composition of the perimysium can occur across different muscles and activity levels, influencing elasticity and resistance to stretch. Pathologically, changes such as fibrosis or thickening of the perimysium can alter muscle mechanics and are observed in certain myopathies and aging. In histology, perimysial tissue is identified by its location surrounding fascicles and by its vascular and neural elements. See also endomysium and epimysium.