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Ch. 10 Muscle Tissue
Martini - Fundamentals of Anatomy & Physiology 11th Edition
Martini, Nath, Bartholomew11th EditionFundamentals of Anatomy & PhysiologyISBN: 9780136874089Not the one you use?Change textbook
All textbooksMartini, Nath, Bartholomew 11th EditionCh. 10 Muscle TissueProblem 7
Chapter 10, Problem 7

Which of the following statements about myofibrils is not correct?
(a) Each skeletal muscle fiber contains hundreds to thousands of myofibrils.
(b) Myofibrils contain repeating units called sarcomeres.
(c) Myofibrils extend the length of a skeletal muscle fiber.
(d) Filaments consist of bundles of myofibrils.
(e) Myofibrils are attached to the plasma membrane at both ends of a muscle fiber.

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1
Step 1: Understand what a myofibril is. Myofibrils are long, cylindrical organelles found within skeletal muscle fibers, composed of repeating units called sarcomeres, which are the functional contractile units of muscle.
Step 2: Analyze statement (a): Each skeletal muscle fiber contains hundreds to thousands of myofibrils. This is correct because muscle fibers are packed with many myofibrils to facilitate contraction.
Step 3: Analyze statement (b): Myofibrils contain repeating units called sarcomeres. This is correct since sarcomeres are the structural units within myofibrils responsible for muscle contraction.
Step 4: Analyze statement (c): Myofibrils extend the length of a skeletal muscle fiber. This is true because myofibrils run longitudinally along the entire length of the muscle fiber.
Step 5: Analyze statement (d): Filaments consist of bundles of myofibrils. This is incorrect because filaments (actin and myosin) are the smaller protein structures that make up myofibrils, not the other way around. Myofibrils are made up of filaments, not filaments made of myofibrils.

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Key Concepts

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

Structure and Composition of Myofibrils

Myofibrils are long, cylindrical organelles found within skeletal muscle fibers, composed of repeating units called sarcomeres. These sarcomeres contain the contractile proteins actin and myosin, which are responsible for muscle contraction. Understanding their structure is key to identifying correct statements about myofibrils.
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Relationship Between Myofibrils and Muscle Fibers

Each skeletal muscle fiber contains hundreds to thousands of myofibrils that run parallel along the length of the fiber. Myofibrils do not bundle filaments; rather, they themselves are bundles of filaments. Recognizing this relationship helps clarify misconceptions about muscle fiber organization.
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Attachment and Orientation of Myofibrils

Myofibrils extend the entire length of a muscle fiber and are anchored at the ends to the plasma membrane (sarcolemma) via structures like the Z-discs. This attachment allows force generated by sarcomere contraction to be transmitted to the muscle fiber and ultimately to tendons.
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Related Practice
Textbook Question

Identify the structures in the following figure.

a. ___

b. ___

c. ___

d. ___

e. ___

f. ___

g. ___

h. ___

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Textbook Question

An action potential can travel quickly from one cardiac muscle cell to another because of the presence of

(a) Gap junctions

(b) Tight junctions

(c) Intercalated discs

(d) Both a and c

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Textbook Question

What structural feature of a skeletal muscle fiber propagates action potentials into the interior of the cell?

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Textbook Question

What three layers of connective tissue are part of each muscle? What functional role does each layer play?

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