Muscle Tissue Classification
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Questions and Answers

What type of muscle is found in the wall of the heart and the proximal portions of the aorta and the venae?

  • Smooth muscle
  • Skeletal muscle
  • Cardiac muscle (correct)
  • Voluntary striated muscle

    • What is a characteristic feature of cardiac muscle?

  • Voluntary contraction
  • Spontaneous contraction (correct)
  • Multinucleated cells
  • Non-striated cells

    • What is unique about the structure of cardiac muscle cells?

  • They have a branched structure
  • They have multiple nuclei
  • They have a single nucleus located centrally (correct)
  • They are non-striated

    • What is the function of intercalated disks in cardiac muscle?

    <p>To facilitate ionic continuity between adjacent cells</p> Signup and view all the answers

    What is a characteristic feature of smooth muscle?

    <p>Non-striated cells</p> Signup and view all the answers

    Where is smooth muscle typically found?

    <p>In blood vessels and hollow viscera</p> Signup and view all the answers

    What is a structural feature of smooth muscle cells?

    <p>They have a spindle shape</p> Signup and view all the answers

    What is true about the sarcoplasmic reticulum in cardiac muscle?

    <p>It is not well-developed</p> Signup and view all the answers

    What is the function of smooth muscle in relation to fibroblast activity?

    <p>Supplementing collagen synthesis</p> Signup and view all the answers

    What is the shape of smooth muscle cells?

    <p>Spindle</p> Signup and view all the answers

    What is the location of the nucleus in smooth muscle cells?

    <p>Central, single nucleus</p> Signup and view all the answers

    What is the function of troponin C in skeletal muscle contraction?

    <p>Moving tropomyosin and exposing actin for myosin binding</p> Signup and view all the answers

    What type of cell junction is found in cardiac muscle?

    <p>Intercalated disk</p> Signup and view all the answers

    What is the mechanism of contraction in smooth muscle cells?

    <p>Actin-myosin binding with phosphorylation by MLCK</p> Signup and view all the answers

    What is the characteristic of skeletal muscle cells?

    <p>Being very long, multinucleated, and having cross-striations</p> Signup and view all the answers

    What is the function of the sarcoplasmic reticulum in skeletal muscle cells?

    <p>To store and release calcium ions</p> Signup and view all the answers

    What is the term for the cell membrane of skeletal muscle cells?

    <p>Sarcolemma</p> Signup and view all the answers

    What is the characteristic of cardiac muscle cells?

    <p>Being branched and having intercalated discs</p> Signup and view all the answers

    What is the name of the structure that surrounds individual muscle fibers?

    <p>Endomysium</p> Signup and view all the answers

    What is the term for the functional unit of skeletal muscle cells?

    <p>Sarcomere</p> Signup and view all the answers

    What is the characteristic of smooth muscle cells?

    <p>Having a lack of striation and being involuntary</p> Signup and view all the answers

    What is the component of the sarcomere that is bisected by the M line?

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

    What is the function of the globular heads of a myosin molecule?

    <p>To form cross bridges and have ATPase activity</p> Signup and view all the answers

    What is the composition of thin filaments?

    <p>Actin, tropomyosin, and troponin</p> Signup and view all the answers

    What is the function of the TnI subunit of troponin?

    <p>To inhibit the actin-myosin interaction</p> Signup and view all the answers

    What is the function of the sarcoplasmic reticulum?

    <p>To store calcium ions</p> Signup and view all the answers

    What is the structure composed of a T tubule and two terminal cisternae?

    <p>A triad</p> Signup and view all the answers

    What is the mechanism of muscle contraction?

    <p>The sliding filament hypothesis</p> Signup and view all the answers

    What is the step that occurs after the impulse reaches the sarcolemma?

    <p>The impulse is conducted rapidly through the T tubules</p> Signup and view all the answers

    What is the final step in the mechanism of muscle contraction?

    <p>Myosin heads pivot, moving thin filaments toward the sarcomere center</p> Signup and view all the answers

    Study Notes

    Classification of Muscles

    • Skeletal muscle:
      • Very long, multinucleated cells
      • Cross-striations
      • Voluntary, forceful
    • Cardiac muscle:
      • Branched
      • Cross-striations
      • Intercalated discs
      • Involuntary, rhythmic
    • Smooth muscle:
      • Fusiform cells
      • Lack striations
      • Involuntary, slow

    Specialized Terms

    • Sarcolemma: Cell membrane
    • Sarcoplasm: Cytoplasm
    • Sarcoplasmic reticulum: SER

    Organization of Skeletal Muscle

    • Epimysium: Dense connective tissue surrounding entire muscle
    • Perimysium: Thin connective tissue surrounding bundles of muscle fibers (fascicle)
    • Endomysium: Reticular fiber and fibroblast surrounding individual muscle fibers

    Structure of Skeletal Muscle Fibers

    • Long, cylindrical cell: 10-100µm in diameter and 1-40mm in length
    • Multinucleated, with nuclei lying beneath sarcolemma
    • Cross-striations: alternating dark and light bands
    • Myofibrils: Thread-like structures arranged in parallel in muscle fibers

    Myofibrils

    • Long, cylindrical filamentous bundles
    • Parallel to the long axis of muscle fibers
    • 1-2µm in diameter
    • Alternate A bands and I bands
    • I band is bisected by a dark transverse line, Z line
    • A band: light zone present, H band, bisected by M line
    • Sarcomere: The unit of structure and function of muscle fibers
    • Myofilaments: Thick and thin filaments

    Thick Filaments

    • Occupy A band
    • Made up of myosin molecules
    • A single myosin molecule has a rod and two globular heads
    • The rods overlap; the globular heads forming cross-bridges and having ATPase activity

    Thin Filaments

    • One end inserted into the Z line, the other extends into the A band
    • Composed of actin, tropomyosin, and troponin
    • Actin: Globular monomers (G-actin) and filamentous polymers (F-actin)
    • Tropomyosin: A long, thin molecule containing two polypeptide chains
    • Troponin: A complex of three subunits: TnT (attaches to tropomyosin), TnI (inhibits actin-myosin interaction), and TnC (binds calcium ions)

    Transverse Tubules and Sarcoplasmic Reticulum

    • Transverse tubules: Sarcolemma tubular infoldings at A- and I-band boundaries, responsible for rapid conduction of impulses
    • Sarcoplasmic reticulum: Stores calcium ions, located between two adjacent T-tubules, terminal cisternae

    Mechanism of Contraction

    • Sliding filament hypothesis
    • Impulse of NF: Calcium binds to TnC of troponin, myosin combines with actin to form cross-bridges, myosin heads pivot, moving thin filaments towards the sarcomere center

    Cardiac Muscle

    • Found in the wall of the heart and proximal portions of the aorta and venae
    • Involuntary, striated muscle
    • Contracting spontaneously and displaying a rhythmic beat
    • LM structure:
      • Short column and branched
      • One or two centrally placed nucleus
      • Show cross-striations and myofibrils, but less distinct
      • Intercalated disks link cells to one another
    • Ultrastructure:
      • Discrete myofibril bundles not present
      • Larger T-tubules at Z-line level
      • Sarcoplasmic reticulum: Not well-developed, small terminal cisternae
      • Dyads: T-tubule and terminal cisternae on one side
      • More mitochondria, glycogen, and lipid droplets

    Smooth Muscle

    • Seen in blood vessels and hollow viscera (visceral muscle)
    • Arranged in layers
    • Enclosed by a network of type I and type III collagen fibers
    • Non-striated cells
    • LM structure:
      • Spindle in shape, with an oval, centrally located nucleus
      • A range of diameters
      • Without striations
    • EM structure:
      • Gap junctions
      • Caveolae
      • A rudimentary sarcoplasmic reticulum
      • Myofibrillar arrays
      • Thick filaments
      • Thin filaments
      • Dense body: Works as Z line
      • Intermediate filament: Desmin, attaches to dense bodies

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    Description

    This quiz covers the classification of muscle tissue based on their structure and function, including skeletal, cardiac, and smooth muscle characteristics.

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