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Muscle Tissues and Cells

Muscle tissue has one major function and is comprised of only one type of cell. Muscle cells are specialized cells that have the ability to contract; thus muscle tissue is exclusively involved with movement of one kind or another. Muscle tissues are grouped into three major types based on the appearance of the tissue and its interaction with the nervous system.
  • Skeletal muscle: Skeletal muscles have a striped or striated appearance and are controlled voluntarily, or consciously. These muscles are almost always connected to bones, directly or via tendons. Skeletal muscles make up between 20 and 40% of the mass of the entire body, and usually exist in antagonistic pairs. All of the muscles under conscious control, and therefore the ones we usually think about, are skeletal muscles. Examples are the biceps and triceps in the upper arm.
  • Cardiac muscle: Cardiac muscle tissue is found only in the heart, and has the distinction of being the only muscle tissue in the body that appears striated but is controlled involuntarily. Also called the myocardium, the importance of this type of muscle tissue cannot be overstated; if it fails to function properly for only a few minutes, death can occur. If a portion of the myocardium does not receive a sufficient supply of oxygen, a myocardial infarction, or “heart attack”, may result.
  • Smooth muscle: Smooth muscle, as its name implies, does not appear striped, but looks uniformly smooth, and is always controlled involuntarily. Due to this fact, we are often unaware of the actions of smooth muscles within our bodies. Smooth muscle surrounds the walls of hollow internal organs, such as those in the digestive and urogenital systems. Rhythmic contractions of smooth muscles provide the driving force for the unidirectional passage of food through the gastrointestinal tract (called peristalsis), and are largely responsible for blood circulation in veins, where the blood pressure originating from the heart has all but dissipated.

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