Role of Ca2 in Muscle Contraction

In a relaxed muscle, when tropomyosin blocks the attachment of cross bridges to actin, the concentration of Ca2+ in the sar-coplasm (cytoplasm of muscle cells) is very low. When the muscle cell is stimulated to contract, mechanisms that will be discussed shortly cause the concentration of Ca2+ in the sar-coplasm to quickly rise. Some of this Ca2+ attaches to troponin, causing a conformational change that moves the troponin complex and its attached tropomyosin out of the way so that the cross bridges can attach to actin (fig. 12.14). Once the attachment sites on the actin are exposed, the cross bridges can bind to actin, undergo power strokes, and produce muscle contraction.

The position of the troponin-tropomyosin complexes in the thin filaments is thus adjustable. When Ca2+ is not attached to troponin, the tropomyosin is in a position that inhibits attachment of cross bridges to actin, preventing muscle contraction. When Ca2+ attaches to troponin, the troponin-tropomyosin complexes shift position. The cross bridges can then attach to actin, produce a power stroke, and detach from actin. These contraction cycles can continue as long as Ca2+ is attached to troponin.

Chapter Twelve

Clinical Investigation Clues

Remember that Maria has muscle pain and fatigue, and that her body seems stiff. Further, she has an elevated blood concentration of Ca2+.

■ How might the high blood Ca2+ be related to Maria's symptoms?

■ What might cause an elevated blood Ca2+ (hint—see chapter 11 or 19).

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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  • travis
    What is the role of Ca2 in muscle contractions?
    6 years ago
  • ria
    What is the functioning of Ca2 in skeletal muscle contraction?
    6 years ago
  • celendine
    What is the role of ca2 in muscle contaction?
    3 years ago
  • janice
    What is the role of Ca2 in the control of muscle contraction?
    2 years ago
  • berhane
    What dKnow the 2 locations where ↑Ca2 is required for physiology of muscle contraction?
    4 months ago
    Which of the following best describes the role of ca2 in muscle contraction?
    22 days ago

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