BIOLOGY:CONCEPTS+APPL.(LOOSELEAF)
10th Edition
ISBN: 9781305967359
Author: STARR
Publisher: CENGAGE L
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Chapter 32, Problem 12SA
Summary Introduction
Introduction:
A muscle contraction is initiated by motor signaling pathway. The arrival of the stimulus causes the activation of primary motor cortex in the brain. The motor cortex sends a signal to the brainstem and spinal cord. The activation of motor neurons by the spinal cord initiates the process of muscle contraction.
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A 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.
Stimulation of a muscle fiber by a motor neuron occurs ata. the neuromuscular junction.b. the transverse tubules.c. the myofibril.d. the sarcoplasmic reticulum.e. none of the above.
When 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.
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- 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_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_forwardA skeletal muscle motor unit A.Is the number of muscle cells innervated by one motor neuron. B.Is the number of motor neurons innervating one muscle cell. C.Size determines the ability to control a muscle D.Size determines how much a muscle contracts at any one time.arrow_forward
- 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.arrow_forwardAll of the following characteristics apply to skeletal muscle except a. They are striated. b. They are multinucleated. c. They are voluntary. d. They contain intercalated discs. e. They are attached to the skeleton by means of tendons.arrow_forwardUnlike skeletal muscle cells, cardiac muscle cells________." A do not use the sliding filament mechanism of contraction B are not striated C do not rely on an influx of Ca+2 for contraction to occur D do not require neural stimulation to contractarrow_forward
- In a skeletal muscle fiber, Ca2+ is released from a. ACh receptors. b. the motor end plate. c. the sarcoplasmic reticulum. d. the sarcolemma and T-tubules.arrow_forwardGraph A in this diagram represents A) summation and tetanus of a smooth muscle fibre. C) a simple skeletal muscle twitch c) summation and tetanus of a skeletal muscle fibre. D)simple smooth muscle twitch.arrow_forwardWhat happens to sarcomeres when actin and myosin filaments in a muscle fiber interact during the contraction phase? A) sarcomeres usually fatigue B) sarcomeres usually get shorter C) sarcomeres usually get longer D) sarcomeres stay the samearrow_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_forwardmuscle cells are made up of? A. Z bars b. actin c. myosin d. myofibrilsarrow_forwardThe muscles of a professional sprinter are most likely to have ________.a. 80 percent fast-twitch muscle fibers and 20 percent slow-twitch muscle fibersb. 20 percent fast-twitch muscle fibers and 80 percent slow-twitch muscle fibersc. 50 percent fast-twitch muscle fibers and 50 percent slow-twitch muscle fibersd. 40 percent fast-twitch muscle fibers and 60 percent slow-twitch muscle fibersarrow_forward
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