Photograph by Rich Reid. Tundras are among Earth's coldest, harshest biomes. Tundra ecosystems are treeless regions found in the Arctic and on the tops of mountains, where the climate is cold and windy and rainfall is scant. Tundra lands are snow-covered for much of the year, until summer brings a burst of wildflowers.
Muscle is a soft tissue found in most animals. Muscle cells contain protein filaments of actin and myosin that slide past one another, producing a contraction that changes both the length and the shape of the cell. The statement that the tongue is the strongest muscle in the body appears frequently in lists of surprising facts, but it is difficult to find any definition of strength that would make this statement true. 2  Note that the tongue consists of eight muscles, not one.
There are three types of muscle tissue (more than 600 muscles) in the body including skeletal muscle, cardiac muscle and smooth muscle. Skeletal muscle is the kind of muscle that helps to create movement in the body. The skeletal muscles make up 40 percent of a person's body weight. Cardiac muscle is involuntary muscle in the body and make up the muscles found in the heart cavity. Smooth muscle is also an involuntary muscle, but it makes up the walls of organs, blood vessels and respiratory passageways.