Human Physiology
Human Physiology
15th Edition
ISBN: 9781259864629
Author: Fox, Stuart Ira
Publisher: Mcgraw-hill Education,
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Chapter 12, Problem 21RA

Explain why the myosin heads don't bind to the actin when the muscle is at rest. Then, provide a step-by-step explanation of how depolarization of the muscle fiber plasma membrane by ACh leads to the binding of the myosin heads to actin. (That is, explain excitation-contraction coupling.)

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Describe the contraction of a muscle fiber, starting with what events take place at the neuromuscular junction, explaining how depolarization along the length of the sarcolemma occurs, the role of calcium (where it is released, what it binds to, etc.), and the events that occur after calcium binds to troponin.  Draw a few simple, labelled diagrams of a neuromuscular junction and sarcomere and outline the steps of excitation-contraction coupling, including power stroke, recovery stroke, formation of cross bridges, role of ATP, etc.
As mentioned in class, one additional major use of ATP in skeletal muscle (besides powering the myosin heads) is the recycling of calcium ions back into the sarcoplasmic reticulum after depolarization. The resting concentration of Ca++ in the muscle cell cytoplasm is about 50-100 nM, and the spike concentration after depolarization is about 10-20 μΜ. a) Consider a single sarcomere. What is the number of free calcium ions within the sarcomere at rest? What is the number of free calcium ions after depolarization? b) The major ion pump responsible for calcium ion recycling is SERCA (sarco/endoplasmic reticulum calcium ATPase). SERCA uses one molecule of ATP to pump two calcium ions, and the resting level can be restored in about 10-20 ms. How many molecules of ATP are used in a single sarcomere for pumping calcium in a single "twitch"? c) Assume that a single "twitch" is sufficient to drive one sarcomere from its fully extended length (about 2.5 µm) to its fully contracted length (about 1…
Briefly describe why contraction of the muscle cell is called “sliding filament theory” (what is sliding?) and what do we mean by “excitation-contraction coupling?”  (What is being excited, and what is coupled?)

Chapter 12 Solutions

Human Physiology

Ch. 12 - Explain how graded contractions and smooth,...Ch. 12 - Prob. 6bCPCh. 12 - Prob. 7aCPCh. 12 - Describe the relationship between the resting...Ch. 12 - Prob. 8CPCh. 12 - Prob. 9CPCh. 12 - Explain the different causes of muscle fatigue...Ch. 12 - Prob. 11CPCh. 12 - Prob. 12aCPCh. 12 - Describe all of the events that occur from the...Ch. 12 - Prob. 13CPCh. 12 - Explain the significance of reciprocal innervation...Ch. 12 - Describe the functions of gamma motor neurons and...Ch. 12 - Explain how cardiac muscle differs from skeletal...Ch. 12 - Contrast the structure of a smooth muscle cell...Ch. 12 - Distinguish between single-unit and multiunit...Ch. 12 - Describe the events by which depolarization of a...Ch. 12 - Prob. 1RACh. 12 - Prob. 2RACh. 12 - Prob. 3RACh. 12 - Prob. 4RACh. 12 - Prob. 5RACh. 12 - Prob. 6RACh. 12 - Prob. 7RACh. 12 - Electrical excitation of a muscle fiber most...Ch. 12 - The energy for muscle contraction is most directly...Ch. 12 - Prob. 10RACh. 12 - Prob. 11RACh. 12 - Prob. 12RACh. 12 - Which of these types of muscle cells are not...Ch. 12 - Prob. 14RACh. 12 - In an isotonic muscle contraction,...Ch. 12 - Prob. 16RACh. 12 - Prob. 17RACh. 12 - Prob. 18RACh. 12 - Using the concept of motor units, explain how...Ch. 12 - Prob. 20RACh. 12 - Explain why the myosin heads don't bind to the...Ch. 12 - Using the sliding filament theory of contraction,...Ch. 12 - Prob. 23RACh. 12 - Prob. 24RACh. 12 - Prob. 25RACh. 12 - What changes occur in muscle metabolism as the...Ch. 12 - Prob. 27RACh. 12 - Compare cardiac muscle, single-unit smooth muscle,...Ch. 12 - Your friend eats huge helpings or pasta for two...Ch. 12 - Prob. 30RACh. 12 - Prob. 31RACh. 12 - How is electrical excitation of a skeletal muscle...Ch. 12 - Prob. 33RACh. 12 - Prob. 34RACh. 12 - Prob. 35RACh. 12 - Prob. 36RACh. 12 - Refer to figure 12.22 to answer the following...Ch. 12 - Refer to figure 12.22 to answer the following...Ch. 12 - Prob. 39RACh. 12 - Refer to figure 12.22 to answer the following...
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