Muscles in the Human Body
The musculoskeletal system is made up of bones, joints, and muscles. This system gives the body form and support, and protects the body while allowing it to move. Basically, the muscles in this system perform three important body functions: the movement of body parts, maintenance of body parts, and production of body heat. These muscles all consist of a mass of protein fibers grouped together, and most are of mesodermal origin. And almost all of the muscle fibers you will ever have or need were present at birth. Nearly half of your body mass is muscles, the largest and strongest being in the shoulders, upper arms, hips, and thighs. There are over five hundred muscles in the human body. Muscle fibers are basically classified according to their size and speed of contraction. There are three main types of muscles. The first is skeletal. Skeletal muscle makes up the largest mass of muscle in the body, and is the type of muscle that is attached to bones and moves the skeleton in a conscious control, so therefore it is a voluntary muscle. Its contractions are short and strong, providing the force needed for movement. The muscle contractions produce and provide some heat needed in the body. Skeletal muscle tissue is made up of smaller fibers called myofibrils. These myofibrils are composed of even smaller protein filaments. These filaments can be either thick or thin. The thick filaments are made of the protein myosin, and the thin filaments are made of the protein actin. The arrangement of the myosin and actin gives skeletal muscle its striated (or striped) appearance. Each section of a myofibril is called a sarcomere, and is the functional unit of muscle. How muscles contract is directly related to their structure. The sliding filament theory is an explanation of how muscle contractions occur. This theory states that the actin filaments within the sarcomere slide toward one another during contraction. But, the myosin filaments don’t move. The second