31) Which of the following statements is TRUE regarding skeletal-muscle contract

Question

31) Which of the following statements is TRUE regarding skeletal-muscle contraction? A) Binding of myosin to actin takes place when [Ca2-] increases in the cytosol. one cross-bridge cycle can occur when the (Ca2*] is elevated in the cytosol; in order to undergo a second cycle, [Ca2+] must be sequestered in the sarcoplasmic reticulum and released again. C) A single twitch in skeletal muscle lasts the same length of time as the action potential that causes it. D) The powerstroke of the cross-bridge cyele occurs simutaneously with ATP being hyrolyzed E) ATP hydrolysis products must be removed from myosin before it can bind to actin. into ADP and Pi 32) What is the definition of a "motor unit"? A) a single muscle fiber plus all of the motor neurons that innervate it B) all of the muscles that affect the movement of any given joint C) a single motor neuron plus all the muscle fibers it innervates D) a pair of antagonistic muscles E) all of the motor neurons supplying a single muscle 33) What is the function of the transverse tubules in a skeletal-muscle fiber? A) They allow action potentials to propagate deep into the center of skeletal muscle cells. C) They run in parallel with the myofibrils, and have abundant Ca2+-ATPase proteins for i Ca2+ back into the sarcoplasmic reticulum. pumping D) They store the calcium ions that are the main source of activation for the cross-bridge cycle. E) They form the Z lines that mark the end of each sarcomere. 34) Which of the following statements regarding myosin in skeletal muscle is TRUE? A) The rate of ATP hydrolysis by myosin is the same in all types of skeletal muscle B) Troponin covers the binding site on myosin molecules until Ca2- binds to troponin to remove it from its blocking position. C) Myosin cross-bridge heads contain two binding sites, one for actin and one for tropomyosin. D) All of the myosin cross-bridge heads in a thick filament are oriented and rotate in the same direction. E) Myosin is an ATPase. 35) Compared to typeI (slow oxidative) skeletal muscle fibers, how are type llb (fast-glycolytic) skeletal muscle fibers different? A) Type llb fibers fatigue more readily. B) Type llb fibers are smaller in diameter. C) Type lIb fibers have more abundant mitochondria. D) Type llb fibers have more abundant myoglobin. E) Type llb motor units contain fewer fibers per alpha motor neuron.

Explanation / Answer

31. (A) Binding of myosin to actin takes place when [Ca2+] increases in the cytosol.

32. (A) a single motor neuron plus all the muscle fibers it innervates.

33. (A) They allow action potentials to propagate deep into the center of skeletal muscle cells.

34. (E) Myosin is an ATPase.

35. (A) Type IIb fibers fatigue more readily.

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