Moving part away from midline

chapter objectives

After you have studied this chapter, you should be able to

1. Describe how connective tissue is part of the structure of a skeletal muscle.

2. Name the major parts of a skeletal muscle fiber and describe the function of each part.

3. Explain the major events that occur during muscle fiber contraction.

4. Explain how energy is supplied to the muscle fiber contraction mechanism, how oxygen debt develops, and how a muscle may become fatigued.

5. Distinguish between fast and slow muscle fibers.

6. Distinguish between a twitch and a sustained contraction.

7. Describe how exercise affects skeletal muscles.

8. Explain how various types of muscular contractions produce body movements and help maintain posture.

9. Distinguish between the structures and functions of a multiunit smooth muscle and a visceral smooth muscle.

10. Compare the contraction mechanisms of skeletal, smooth, and cardiac muscle fibers.

11. Explain how the locations of skeletal muscles help produce movements and how muscles interact.

12. Identify and locate the major skeletal muscles of each body region and describe the action of each muscle.

-troph, well fed: muscular hypertrophy—enlargement of muscle fibers. voluntar-, of one's free will:

voluntary muscle—muscle that can be controlled by conscious effort.

Understanding ^Vo rds calat-, something inserted: intercalated disk— membranous band that connects cardiac muscle cells.

erg-, work: synergist—muscle that works together with a prime mover to produce a movement. fasc-, bundle: /asciculus—

bundle of muscle fibers. -gram, something written:

myogram—recording of a muscular contraction. hyper-, over, more: muscular hypertrophy—enlargement of muscle fibers. inter-, between: intercalated disk—membranous band that connects cardiac muscle cells. iso-, equal: isotonic contraction—contraction during which the tension in a muscle remains unchanged. laten-, hidden: latent period— period between a stimulus and the beginning of a muscle contraction. myo-, muscle: myofibril— contractile fiber of a muscle cell. reticul-, a net: sarcoplasmic reticulum—network of membranous channels within a muscle fiber. sarco-, flesh: sarcoplasm— substance (cytoplasm) within a muscle fiber. syn-, together: synergist—muscle that works with a prime mover to produce a movement. tetan-, stiff: tetanic contraction— sustained muscular contraction. -tonic, stretched: isotonic contraction—contraction during which the tension of a muscle remains unchanged.

ike many things in life, individual muscles aren't appreciated until we see what happens when they do not work. For children with Moebius syndrome, absence of the sixth and seventh cranial nerves, which carry impulses from the brain to the muscles of the face, leads to an odd collection of symptoms.

signs of Moebius syndrome are typically difficulty sucking, excessive drooling, and sometimes crossed eyes. The child has difficulty swallowing and chokes easily, cannot move the tongue well, and is very sensitive to bright light because he or she cannot squint or blink or even avert the eyes. Special bottles and feeding tubes can help the child eat, and surgery can correct eye defects.

Children with Moebius syndrome are slow to reach developmental milestones but do finally walk. As they get older, if they are lucky, they are left with only one symptom, but it is a rather obvious one—inability to form facial expressions.

A young lady named Chelsey Thomas called attention to this very rare condition when she underwent two surgeries that would enable her to smile. In 1995 and 1996, when she was 7 years old, Chelsey had two transplants of nerve and muscle tissue from her legs to either side of her mouth, supplying the missing "smile apparatus." Gradually, she acquired the subtle, and not-so-subtle, muscular movements of the mouth that make the human face so expressive. Chelsey inspired several other youngsters to undergo "smile surgery."

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