The largest oil spill to occur in the United States so far was the Exxon Valdez spill into Prince William Sound, Alaska, in March 1989. The Exxon Valdez, a medium-sized oil tanker, ran aground on a reef to cause this spill of almost 11 million gallons of crude oil.
Sphincters, composed of skeletal muscles, regulate movement through our digestive and urinary systems, thus, controlling swallowing, defecation and even urination. Skeletal muscle contraction generates heat, which helps to maintain body temperature.
Skeletal muscles are composed of striated subunits called sarcomeres, which are composed of the myofilaments actin and myosin. Illustrate the structure of a skeletal muscle fiber. 1  Muscles are composed of long bundles of myocytes or muscle fibers.  Myocytes contain thousands of myofibrils.