The hypodermis separates muscle from skin. It is composed of areolar connective tissue and adipose tissue, provides a pathway for nerves and blood and lymphatic vessels to enter and exit muscles, serves as an insulating layer that reduces heat loss, and protects muscles from physical trauma. Fascia (bandage) is a sheet or broad band of dense connective tissue that supports and surrounds muscles and other organs of the body. Fascia holds together muscles with similar functions; allows free movement of muscles; carries nerves, blood vessels, and lymphatic vessels; and fills spaces between muscles.
Epimysium, the outermost layer of dense connective tissue, encircles the entire muscle. Perimysium is also a layer of dense, irregular connective tissue, but it surrounds groups of 10 to 100 or more muscle fibers, separating them into bundles called fascicles.
Endomysium penetrates the interior of each fascicle and separates individual muscle fibers from one another. The endomysium is a thin sheath of areolar connective tissue.
As the contraction cycle continues, movement of myosin heads applies the force that draws the Z discs toward each other, and the sarcomere shortens. During a maximal muscle contraction, the sarcomere can shorten by as much as half the resting length. The Z discs, in turn, pull on neighboring sarcomeres, shortening the whole muscle fiber, which ultimately leads to shortening of the entire muscle. As the fibers of a skeletal muscle start to shorten, they first pull on their connective tissue coverings (endomysium, perimysium, and epimysium) and tendons. The coverings and tendons become taut, and the tension passed through the tendons pulls on the bones to which they are attached. The result is movement of a part of the body.