Anatomy & Physiology All-in-One For Dummies (+ Chapter Quizzes Online)
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The study of muscles is called myology after the Greek word mys, which means “mouse.” Muscles perform a number of functions vital to maintaining life, including

  • Movement: Skeletal muscles (those attached to bones) convert chemical energy into mechanical work, producing movement ranging from finger tapping to a swift kick of a ball by contracting, or shortening. Reflex muscle reactions protect your fingers when you put them too close to a fire and startle you into watchfulness when an unexpected noise sounds. Many purposeful movements require several sets, or groups, of muscles to work in unison.

  • Vital functions: Without muscle activity, you die. Muscles are doing their job when your heart beats, when your blood vessels constrict, and when your intestines squeeze food along your digestive tract in peristalsis.

  • Antigravity: Perhaps that’s overstating it, but muscles do make it possible for you to stand and move about in spite of gravity’s ceaseless pull. Did your mother tell you to improve your posture? Just think how bad it would be without any muscles!

  • Heat generation: You shiver when you’re cold and stamp your feet and jog in place when you need to warm up. That’s because chemical reactions in muscles result in heat, helping to maintain the body’s temperature.

  • Keeping the body together: Muscles are the warp and woof of your body’s structure, binding one part to another.

  • Joint stability: Muscles and their tendons aid the ligaments to reinforce joints.

  • Supporting and protecting soft tissues: The body wall and floor of the pelvic cavity support the internal organs and protect soft tissues from injury.

  • Sphincters: These muscles encircle openings to control swallowing, defecation, and urination.

As you may remember from studying tissues, muscle cells — called fibers — are some of the longest in the body. Fibers are held together by connective tissue and enclosed in a fibrous sheath called fascia. Some muscle fibers contract rapidly, whereas others move at a leisurely pace.

Generally speaking, however, the smaller the structure to be moved, the faster the muscle action. Exercise can increase the thickness of muscle fibers, but it doesn’t make new fibers. Skeletal muscles have a rich vascular supply that dilates during exercise to give the working muscle the extra oxygen it needs to keep going.

Two processes are central to muscle development in the developing embryo: myogenesis, during which muscle tissue is formed, and morphogenesis, when the muscles form into internal organs. By the eighth week of gestation, a fetus is capable of coordinated movement.

Following are some important muscle terms to know:

  • Fascia: Loose, or areolar, connective tissue that holds muscle fibers together to form a muscle organ

  • Fiber: An individual muscle cell

  • Insertion: The more movable attachment of a muscle

  • Ligament: Dense, regular connective tissue that supports joints and anchors organs

  • Motor nerve: A nerve that stimulates contraction of a muscle

  • Myofibril: Fibrils within a muscle cell that contain protein filaments such as actin and myosin that slide during contraction, shortening the fiber (or cell)

  • Origin: The immovable attachment of a muscle, or the point at which a muscle is anchored by a tendon to the bone

  • Sarcoplasm: The cellular cytoplasm in a muscle fiber

  • Tendon: Connective tissue made up of collagen, a fibrous protein that attaches muscles to bone; allows some muscles to apply their force at some distance from where a contraction actually takes place

  • Tone, or tonus: State of tension present to a degree at all times, even when the muscle is at rest

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