There are about 600 voluntary muscles in the body. Each muscle is made up of thousands of long and narrow muscle cells called muscle fibers. These muscle fibers are arranged in bundles and enclosed within a tough layer of connective tissue called epimysium (sarcolema). Every muscle fiber is made up of very large number of microscopic threads called myofibrils. Myofibrils consists of protein molecules called actin and myosin.
