Human Physiology
15th Edition
ISBN: 9781259864629
Author: Fox, Stuart Ira
Publisher: Mcgraw-hill Education,
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Chapter 12, Problem 10RA
Summary Introduction
To determine:
The correct statement about the cross-bridges.
Introduction:
Cross bridge is the most important process involved in muscle contraction. It shows how the actin and filaments move relative to each other. The actin and myosin filaments bind to each other in order to cause sarcomere shortening, hence muscle contraction.
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What event causes a troponin-tropomyosin complex to regain its original shape in muscle relaxation? a. stimulation of ACh receptors b. diffusion of Na+ back into transverse tubules c. return of Ca2+ into the sarcoplasmic reticulum d. breaking of the bond with tropomyosin
What do skeletal muscle contractions share in common with smooth muscle contractions?a. Both types of contractions do not require calcium ions for a contraction to occur.b. Both types of contractions generate little force or a weak force.c. Both types of contractions consume very little ATP.d. Both types of contractions result from thick and thin filaments sliding past one another.
The Sarcomere 2
Thin filaments are often named for which protein?
a. actin
b. myosin
c. troponin
d. tropomyosin
Chapter 12 Solutions
Human Physiology
Ch. 12 - Describe the actions of muscles when they...Ch. 12 - Describe the different levels of muscle structure,...Ch. 12 - Define the terms motor unit and innervation ratio...Ch. 12 - Using the concept of recruitment, explain how...Ch. 12 - With reference to the sliding filament theory,...Ch. 12 - Prob. 3bCPCh. 12 - Describe a cycle of cross-bridge activity during...Ch. 12 - Prob. 4bCPCh. 12 - Use a flowchart to show the sequence of events...Ch. 12 - Prob. 5bCP
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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- What might happen if skeletal muscle lacked tropomyosin? A. The striation pattern would disappear. B. Ca2+ levels in the muscle would decrease. C. Actin and myosin would not be able to form cross-bridges. D. Acetylcholine would not be released into the synaptic cleft. E. Myosin and actin would form cross-bridges whenever ATP is available.arrow_forwardWhat structure on a muscle fiber is composed of largely two varieties of contractile proteins--actin and myosin--which slide past each other during muscle activity to bring about shortening or contraction of muscle cells? A. myofilament B. sarcoplasmic reticulum C. transverse tububle D. sarcomeresarrow_forwardWith regard to muscle contraction, which of the following is an INCORRECT statement with regard to the interactions of filaments that occur in the sarcomere? A. When muscles are relaxed tropomyosin blocks binding sites on actin subunits, which keeps cross-bridges from forming. B. The myosin heads conduct a power stroke motion to slide when bound to actin, to move the "thin" filaments towards the center of the sarcomere. C. During contraction, actin subunits are removed from the ends of the "thin" filaments to shorten actin polymers, thus reducing the length of the sarcomere. D. "Thick" filaments are anchored at the M-line, while "thin" filaments are anchored at the Z-line. E. Numerous myosin heads engage with the actin filaments simultaneously, such that there is no back-slipping during the contraction process.arrow_forward
- The sliding filament mechanism describes the process during which: a. actin and myosin slide relative to each other b. sarcomeres slide relative to each other c. troponin and tropomyosin slide relative to each other d. muscle fibers slide past each otherarrow_forwardWhat happens at a neuromuscular junction?a. An electrical impulse causes the release of a chemical.b. Acetylcholine is released by the muscle cell.c. Acetylcholinesterase is released from the nerve cell.d. A neurotransmitter is released.e. Acetylcholine fits into receptors on the muscle cell.arrow_forwardWhich statement about striated skeletal muscle is true? A. The tension generated by a muscle is invariable. B. Mechanical summation of twitches in a muscle fiber leads to a graded increase in the tension that is above that generated by a single twitch. C. A single action potential arriving at the neuromuscular junction is not sufficient to cause a muscle fiber to twitch. D. Muscle twitches are able to mechanically sum when Ca2+ is quickly and completely removed from the sarcoplasm between action potentials. E. An action potential in the muscle cell activates contraction by releasing Na+ into the sarcoplasm.arrow_forward
- Which of the following statements best describes the sliding filament mechanism of muscle contraction? a. Actin and myosin filaments do not shorten, but rather, slide past each other. b. Actin and myosin filaments shorten and slide past each other. c. As they slide past each other, actin filaments shorten, but myosin filaments do not shorten. d. As they slide past each other, myosin filaments shorten, but actin filaments do not shorten.arrow_forwardThe functions of tropomyosin in skeletal muscle include A. releasing calcium ions after initiation of contraction. B. generating ATP which it passes to the contractile mechanism. C. binding to myosin during contraction. D. acting as a relaxing protein at rest by covering up the sites where myosin binds to actin. E. sliding on actin to produce shortening.arrow_forwardWhat happens in a muscle twitch?a. Myosin grabs a thick myofilament.b. Sarcomeres shorten during the contraction phase.c. ATP is put back in the sarcoplasmic reticulum during the refractory phase.d. A threshold stimulus must be reached before anything will happen.e. Thin myofilaments are pulled toward the center of a sarcomere.arrow_forward
- Myosin binds to actin, then bends. What is ATP needed for next? A. to pump the Ca++ “keys” back into the sarcoplasmic reticulum B. to replace the strap and cover the binding sites C. to give feedback to the neuron that contraction occurred D. to un-bind myosin from actin and re-set for another powerstroke.arrow_forwardWhich is a false statement about skeletal muscle structure?a. A myofibril is composed of multiple muscle fibers.b. Most skeletal muscles attach to bones by connective-tissue tendons.c. Each end of a thick filament is surrounded by six thin filaments.d. A cross-bridge is a portion of the myosin molecule.e. Thin filaments contain actin, tropomyosin, and troponin.arrow_forwardBotulism toxin inhibits the release of acetylcholine at the neuromuscular junctions. What effect does this have on the muscle activity? a. Muscles will contract continuously. b. Muscles will contract sporadically, without conscious control. c. Muscles will not contract because they will not receive nerve stimulation. d. There will be no effect on muscle activityarrow_forward
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