Chapter 6 | The Musculoskeletal System

  1. Figure 6.19 Which of the following statements about bone tissue is false?
    1. Compact bone tissue is made of cylindrical osteons that are aligned such that they travel the length of the bone.
    2. Haversian canals contain blood vessels only.
    3. Haversian canals contain blood vessels and nerve fibers.
    4. Spongy tissue is found on the interior of the bone, and compact bone tissue is found on the exterior.
      Illustration shows a cross-section of a bone. The compact outer part of the bone is made up of cylindrical osteons that run its length. Each osteon is made up of a matrix of lamellae that surround a central Haversian canal. Arteries, veins and nerve fibers run through the Haversian canals. The spongy inner bone consists of porous trabeculae.
      Figure 6.19 Compact bone tissue consists of osteons that are aligned parallel to the long axis of the bone, and the Haversian canal that contains the bone’s blood vessels and nerve fibers. The inner layer of bones consists of spongy bone tissue. The small dark ovals in the osteon represent the living osteocytes. (credit: modification of work by NCI, NIH)

       

  2. Figure 6.37 Which of the following statements about muscle contraction is true?
    1. The power stroke occurs when ATP is hydrolyzed to ADP and phosphate.
    2. The power stroke occurs when ADP and phosphate dissociate from the myosin head.
    3. The power stroke occurs when ADP and phosphate dissociate from the actin active site.
    4. The power stroke occurs when Ca2+ binds the calcium head.
      Illustration shows two actin filaments coiled with tropomyosin in a helix, sitting beside a myosin filament. Each actin filament is made of round actin subunits linked in a chain. A bulbous myosin head with A D P and Pi attached sticks up from the myosin filament. The contraction cycle begins when calcium binds to the actin filament, allowing the myosin head to from a cross bridge. During the power stroke, the myosin head bends and A D P and phosphate are released. As a result, the actin filament moves relative to the myosin filament. A new molecule of A T P binds to the myosin head, causing it to detach. The A T P hydrolyzes to A D P and Pi, returning the myosin head to the cocked position.
      Figure 6.37 The cross-bridge muscle contraction cycle, which is triggered by Ca2+ binding to the actin active site, is shown. With each contraction cycle, actin moves relative to myosin.

       

  3. Figure 6.38 The deadly nerve gas Sarin irreversibly inhibits acetycholinesterase. What effect would Sarin have on muscle contraction?

 

There are four steps in the start of a muscle contraction. Step 1: Acetylcholine released from synaptic vesicles in the axon terminal binds to receptors on the muscle cell plasma membrane. Step 2: An action potential is initiated that travels down the T tubule. Step 3: Calcium ions are released from the sarcoplasmic reticulum in response to the change in voltage. Step 4: Calcium ions bind to troponin, exposing active sites on actin. Cross-bridge formation occurs and muscles contract. Three additional steps are part of the end of a muscle contraction. Step 5: Acetylcholine is removed from the synaptic cleft by acetylcholinesterase. Step 6: Calcium ions are transported back into the sarcoplasmic reticulum. Step 7: Tropomyosin covers active sites on actin preventing cross-bridge formation, so the muscle contraction ends.
Figure 6.38 This diagram shows excitation-contraction coupling in a skeletal muscle contraction. The sarcoplasmic reticulum is a specialized endoplasmic reticulum found in muscle cells.

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