12-L1
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Questions and Answers

Where are smooth muscle fibers mainly found?

  • In the walls of hollow organs (correct)
  • In association with bones
  • In the skeletal muscles
  • In the walls of the heart

    • What is the plasma membrane of muscle cells called?

  • Myofibril
  • Sarcomere
  • Sarcolemma (correct)
  • Myofilament

    • What type of muscle contractions are voluntary?

  • Smooth
  • Skeletal (correct)
  • All muscle types
  • Cardiac

    • What percentage of body weight is attributed to skeletal muscle?

    <p>40% (A)</p> Signup and view all the answers

    Which type of muscle cell has obvious striations?

    <p>Skeletal muscle (C)</p> Signup and view all the answers

    What is the main characteristic of the sarcoplasmic reticulum in cardiac muscle fibers compared to skeletal muscle?

    <p>It is less organized (D)</p> Signup and view all the answers

    Where do cardiac T tubules occur in the muscle fibers?

    <p>At the Z line (B)</p> Signup and view all the answers

    What type of cell is a mature smooth muscle fiber?

    <p>Spindle-shaped (B)</p> Signup and view all the answers

    What ratio of thin to thick filaments is observed in smooth muscle?

    <p>12:1 (B)</p> Signup and view all the answers

    What is a key characteristic of smooth muscle cytoplasm?

    <p>Full of actin and myosin filaments (B)</p> Signup and view all the answers

    What is the cytoplasm of a muscle fiber also known as?

    <p>Sarcoplasm (A)</p> Signup and view all the answers

    Which type of filament is found in the A-bands of myofibrils?

    <p>Myosin (D)</p> Signup and view all the answers

    What is the function of the titin protein in muscle tissues?

    <p>Providing elasticity (C)</p> Signup and view all the answers

    How many molecules of myosin are typically found in a thick myofilament?

    <p>200-500 (D)</p> Signup and view all the answers

    What main proteins are found in the thin filaments?

    <p>F-actin, tropomyosin, troponin (C)</p> Signup and view all the answers

    What type of muscle is cardiac muscle?

    <p>striated involuntary muscle (C)</p> Signup and view all the answers

    What role do collagen fibers play at the muscle-tendon junction?

    <p>They blend with the epimysium and perimysium to prevent muscle tear. (A)</p> Signup and view all the answers

    Which structure in cardiac muscle cells appears as dark lines?

    <p>intercalated discs (A)</p> Signup and view all the answers

    What is a motor unit?

    <p>A single axon and all the muscle fibers it innervates. (C)</p> Signup and view all the answers

    Where are mitochondria located in cardiac muscle cells?

    <p>Both A and B (B)</p> Signup and view all the answers

    What prevents detachment of cardiac muscle fibers from one another during contraction?

    <p>Macula adherens (C)</p> Signup and view all the answers

    Which component of the motor end-plate contains mitochondria and synaptic vesicles?

    <p>The terminal bouton (A)</p> Signup and view all the answers

    Which of these lies directly beneath the presynaptic membrane?

    <p>Continuation of the muscle fiber's basal lamina (C)</p> Signup and view all the answers

    What provides electronic coupling between adjacent cardiac muscle fibers?

    <p>gap junctions (C)</p> Signup and view all the answers

    What does the postsynaptic membrane contain?

    <p>Receptors for acetylcholine (A)</p> Signup and view all the answers

    Which structure is composed of alpha-actinin and is located in the center of the I band?

    <p>Z line (A)</p> Signup and view all the answers

    Which type of myofilament is 5-nm wide and composed primarily of actin?

    <p>Thin filament (A)</p> Signup and view all the answers

    What is the primary function of the sarcoplasmic reticulum in striated muscle cells?

    <p>Sequester calcium ions (B)</p> Signup and view all the answers

    Which band is located in the center of the A band and represents the area where actin is not present?

    <p>H band (C)</p> Signup and view all the answers

    Which component encircles every myofibril near the aligned A-I band boundaries of sarcomeres?

    <p>Transverse tubule (C)</p> Signup and view all the answers

    What is the function of the transverse (T) tubule system in skeletal muscles?

    <p>To bring action potentials into the interior of muscle fibers (C)</p> Signup and view all the answers

    What is the primary characteristic of red fibers (Type I) in skeletal muscles?

    <p>High myoglobin content and ability to sustain slow, steady contractions (C)</p> Signup and view all the answers

    Which type of skeletal muscle fiber is predominant in extraocular muscles?

    <p>White fibers (Type IIb) (D)</p> Signup and view all the answers

    How do intermediate fibers (Type IIa) in skeletal muscles differ from red and white fibers?

    <p>They are a mix of structural and functional characteristics of red and white fibers (A)</p> Signup and view all the answers

    What is the triad in the skeletal muscle fiber structure?

    <p>Specialized complex of two sarcoplasmic reticulum (SR) components and a T tubule (D)</p> Signup and view all the answers

    What type of connective tissue surrounds an entire skeletal muscle?

    <p>Epimysium (D)</p> Signup and view all the answers

    Which of the following connective tissues surrounds each bundle of muscle fibers?

    <p>Perimysium (B)</p> Signup and view all the answers

    Which type of connective tissue is known for its delicate and very thin structure?

    <p>Endomysium (A)</p> Signup and view all the answers

    What structures does loose connective tissue carry to muscle?

    <p>Blood vessels, nerve fibers, and lymphatics (D)</p> Signup and view all the answers

    What cells are responsible for new skeletal muscle fiber formation following muscle injury?

    <p>Satellite cells (A)</p> Signup and view all the answers

    How are the connective tissues in skeletal muscle organized?

    <p>Epimysium around entire muscle, perimysium around fascicles, endomysium around individual fibers (B)</p> Signup and view all the answers

    What is a distinguishing feature of Purkinje fibers under histological preparations?

    <p>Clear empty appearance (D)</p> Signup and view all the answers

    Which muscle type has little regenerative ability beyond early childhood?

    <p>Cardiac muscle (B)</p> Signup and view all the answers

    Which of the following is TRUE regarding smooth muscle repair?

    <p>Smooth muscle contains undifferentiated precursors (D)</p> Signup and view all the answers

    What function are Purkinje fibers specialized for?

    <p>Transmission of excitation (A)</p> Signup and view all the answers

    What is the primary role of Purkinje fibers in the heart?

    <p>Conducting an electrical stimulus to enable coordinated contraction (B)</p> Signup and view all the answers

    Where are Purkinje fibers located?

    <p>In the inner ventricular walls of the heart (B)</p> Signup and view all the answers

    How do Purkinje fibers influence heart rate?

    <p>They do not have a known role in setting heart rate (D)</p> Signup and view all the answers

    What happens when Purkinje fibers generate action potentials faster than usual?

    <p>It can cause premature ventricular contraction or other issues (D)</p> Signup and view all the answers

    What is the backup role of Purkinje fibers in the heart's conduction system?

    <p>To serve as the last resort when other pacemakers fail (A)</p> Signup and view all the answers

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