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Ch. 9 Muscles and Muscle Tissue
Chapter 8, Problem 3

Thick and thin myofilaments have different compositions. For each descriptive phrase, indicate whether the filament is, a. thick or b. thin.  _____ (1) contains actin  _____ (2) contains ATPases  _____ (3) attaches to the Z disc  _____ (4) contains myosin  _____ (5) contains troponin  _____ (6) does not lie in the I band

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1
(1) Identify that actin is a protein found in thin filaments.
(2) Recognize that ATPases are enzymes associated with thick filaments, specifically myosin heads.
(3) Understand that thin filaments attach to the Z disc in the sarcomere structure.
(4) Recall that myosin is the primary protein in thick filaments.
(5) Note that troponin is a regulatory protein found in thin filaments.
(6) Remember that thick filaments do not lie in the I band, as the I band contains only thin filaments.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Myofilament Composition

Myofilaments are the contractile proteins in muscle fibers, primarily categorized into thick and thin filaments. Thick filaments are primarily composed of myosin, while thin filaments consist mainly of actin, along with regulatory proteins such as troponin and tropomyosin. Understanding the distinct compositions of these filaments is crucial for analyzing muscle contraction mechanisms.
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Z Disc and Sarcomere Structure

The Z disc is a structural component of the sarcomere, the basic unit of muscle contraction. Thin filaments attach to the Z disc, while thick filaments are situated in the center of the sarcomere. This arrangement is essential for the sliding filament theory, which explains how muscle contraction occurs through the interaction of thick and thin filaments.
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Role of ATP in Muscle Contraction

ATP (adenosine triphosphate) is vital for muscle contraction as it provides the energy required for the myosin heads to bind to actin and perform the power stroke. Thick filaments contain ATPases, enzymes that hydrolyze ATP to release energy. This energy is crucial for muscle contraction and relaxation, making the understanding of ATP's role essential in muscle physiology.
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Related Practice
Textbook Question
Use the key to classify each of the following described tissue types into one of the four major tissue categories. Key: connective tissue epithelium muscle nervous tissue  _________    (1) Tissue type composed largely of nonliving extracellular matrix; important in protection and support  _________    (2) The tissue immediately responsible for body movement  _________    (3) The tissue that enables us to be aware of the external environment and to react to it  _________    (4) The tissue that lines body cavities and covers surfaces
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The connective tissue covering that encloses the sarcolemma of an individual muscle fiber is called the a. epimysium, b. perimysium, c. endomysium, d. periosteum.
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A fascicle is a a. muscle, b. bundle of muscle fibers enclosed by a connective tissue sheath, c. bundle of myofibrils, d. group of myofilaments.
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The function of the T tubules in muscle contraction is to a. make and store glycogen, b. release Ca²⁺ into the cell interior and then pick it up again, c. transmit the action potential deep into the muscle cells, d. form proteins.
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The sites where the motor nerve impulse is transmitted from the nerve endings to the skeletal muscle cell membranes are the a. neuromuscular junctions, b. sarcomeres, c. myofilaments, d. Z discs.
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Contraction elicited by a single brief stimulus is called a. a twitch, b. temporal summation, c. multiple motor unit summation, d. fused tetanus.
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