BIOLOGY:CONCEPTS+APPL.(LOOSELEAF)
10th Edition
ISBN: 9781305967359
Author: STARR
Publisher: CENGAGE L
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Chapter 32, Problem 2SA
Summary Introduction
Introduction:
A mature skeletal muscle consists of thousands of muscle fibers which are known as myofibrils. These are threadlike proteins which are arranged in identical contractile units called sarcomeres. The thick filament of the sarcomere has a motor protein called myosin and the thin filament has actin as a motor protein.
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Muscle relaxation occurs when ________. a. calcium ions are actively transported out of the sarcoplasmic reticulum b. calcium ions diffuse out of the sarcoplasmic reticulum c. calcium ions are actively transported into the sarcoplasmic reticulum d. calcium ions diffuse into the sarcoplasmic reticulum
Which of the following statements about the Ca2+ release channels in the sarcoplasmic reticulum is false? a.They are also called ryanodine receptors. b.They are one-tenth the size of the voltage-gated Ca 2+channels. c.They are opened by Ca2+release channels in the transverse tubules. d.They permit Ca 2+ to diffuse into the sarcoplasm from the sarcoplasmic reticulum.
If a muscle cell had very short T-tubules, how much tension would the muscle fiber create, relative to a normal muscle fiber? Assume sarcoplasmic reticulum can still react to activity at the neuromuscular junction.
a)Less tension would be created.
b) No difference in tension creation.
c) More tension would be created.
d) No tension would be created.
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- 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_forwardWhen sarcomeres contract during muscle contraction, which of the following occurs? A. The myosin filaments lengthen. B. The myosin filaments "walk" along the actin microfilaments. C. The myosin filaments shorten. D. The actin filaments shorten.arrow_forwardWhat 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 tropomyosinarrow_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_forwardNervous stimulation of musclesa. occurs at a neuromuscular junction.b. results in an action potential that travels down the T system.c. causes calcium to be released from expanded regions of the sarcoplasmic reticulum.d. All of these are correctarrow_forwardWhich of the following statements is true?a. Fast fibers have a small diameter.b. Fast fibers contain loosely packed myofibrils.c. Fast fibers have large glycogen reserves.d. Fast fibers have many mitochondriaarrow_forward
- Which of the following changes takes place when a skeletal muscle contracts?A. Z discs move farther apart.B. Actin filaments contract.C. Myosin filaments contract.D. Sarcomeres become shorter.arrow_forwardA bacterial toxin is known to block the release of ACh at the motor end plate of skeletal muscle. Consequently, a. the skeletal muscle contracts with increasing force. b. the skeletal muscle contracts with increasing frequency. c. the ability to stimulate the muscle is impaired. d. other neurotransmitters would stimulate the muscle.arrow_forwardRigor mortis occurs following death because a. tropomyosin remains over the myosin binding sites of actin. b. myosin heads attach to actin and are not released due to lack of ATP. c. the myosin becomes misshapen. d. all of the Ca2+ remains within the sarcoplasmic reticulum.arrow_forward
- During contraction, the bulk of calcium comes from: A. sarcomere B. sarcoplasm C. sarcoplasmic reticulum D. sarcolemma Coming off of the M line are _________ fibers and extending off of the Z line are __________ fibers. A. troponin; tropomyosin B. actin; myosin C. myosin; actin D. tropomyosin; actin E. myosin; tropomyosinarrow_forwardWhat does ATP binding to myosin head triggers? a. Its association with microtubules b. Its dissociation from actin microfilament c. Conformational change and rotation of myosin head d. Its association with actin microfilamentarrow_forwardIf a muscle cell’s sarcoplasmic reticulum had little to no Ca2+, could the muscle cell still produce an electrical impulse, and would the muscle cell still contract? Explain.arrow_forward
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