Cardiac Muscle Structure and Function
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Questions and Answers

What is the typical structure formation at the junctions between terminal cisterns and T-tubules in smooth muscle cells?

  • Pentad
  • Tetrad
  • Dyads (correct)
  • Triads

    • What is the primary function of smooth muscle cells in the body?

  • Slow and steady contraction (correct)
  • Maintaining posture and balance
  • Generating high forces for brief periods
  • Rapid contraction and relaxation

    • Where are smooth muscle cells typically found in the body?

  • Nervous system and adipose tissue
  • Cardiac muscle and epithelial tissue
  • Blood vessels, digestive, respiratory, urinary, and reproductive tracts and their associated organs (correct)
  • Skeletal muscles and skin

    • What is the shape of smooth muscle cells?

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

    What type of junctions connect smooth muscle cells together?

    <p>Gap junctions</p> Signup and view all the answers

    What are the small invaginations of the plasmalemma in smooth muscle cells called?

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

    How do actin filaments differ between smooth muscle cells and striated muscle cells?

    <p>Actin filaments are not associated with troponin and tropomyosin in smooth muscle cells</p> Signup and view all the answers

    What is the function of dense bodies in smooth muscle cells?

    <p>Transmission of contractile force</p> Signup and view all the answers

    What type of junctions allow smooth muscle cells to contract synchronously?

    <p>Gap junctions</p> Signup and view all the answers

    What is the function of gap junctions in the intercalated disc?

    <p>To promote rapid impulse conduction through many cardiac muscle cells simultaneously</p> Signup and view all the answers

    Which of the following hormones stimulates smooth muscle contraction in the uterus?

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

    What is the main difference in the structure of cardiac muscle cells compared to skeletal muscle cells?

    <p>Cardiac muscle cells have a centrally located nucleus, while skeletal muscle cells are multinucleated</p> Signup and view all the answers

    What type of muscle cells can supplement fibroblast activity by synthesizing collagen, elastin, and proteoglycans?

    <p>Smooth muscle cells</p> Signup and view all the answers

    What is the primary function of varicosities in autonomic nerves?

    <p>To form synapses with smooth muscle fibers</p> Signup and view all the answers

    What is the primary source of energy for cardiac muscle cells?

    <p>Triglycerides stored in lipid droplets</p> Signup and view all the answers

    What is the function of desmosomes in the intercalated disc?

    <p>To provide strong intercellular adhesion during contractions</p> Signup and view all the answers

    Which of the following is NOT a characteristic of smooth muscle?

    <p>Well-defined neuromuscular junctions</p> Signup and view all the answers

    What is the main difference between the ventricular and atrial T-tubules?

    <p>Ventricular T-tubules are larger and penetrate the sarcoplasm to reach the Z discs</p> Signup and view all the answers

    What type of filaments are composed of desmin and attach to dense bodies in smooth muscle cells?

    <p>Intermediate filaments</p> Signup and view all the answers

    What is the percentage of cell volume occupied by mitochondria in cardiac muscle cells?

    <p>30-40%</p> Signup and view all the answers

    What is the characteristic of cardiac muscle contraction compared to skeletal muscle contraction?

    <p>Cardiac muscle contraction is involuntary, vigorous, and rhythmic, while skeletal muscle contraction is voluntary, weak, and irregular</p> Signup and view all the answers

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

    <p>The sarcoplasmic reticulum is less well-organized in cardiac muscle cells</p> Signup and view all the answers

    Study Notes

    Cardiac Muscle

    • Composed of elongated, branched cells connected by intercalated discs
    • Cells are 5-30 μm in diameter and 85-120 μm in length, with a single centrally located nucleus
    • Cardiac muscle is striated by transverse lines, representing intercalated discs between adjacent cells
    • Intercalated discs consist of desmosomes and fascia adherens, providing strong intercellular adhesion during contractions
    • Gap junctions in intercalated discs provide ionic continuity between cells, promoting rapid impulse conduction and contraction of many adjacent cells as a unit
    • Contractile process is similar to skeletal muscle cells
    • Source of energy is mitochondria, which occupy up to 40% of the cell volume, with fatty acids as the main fuel
    • Ventricles are thicker than atria, with ventricular T-tubules being larger and penetrating the sarcoplasm to reach the Z discs
    • Sarcoplasmic reticulum is less well-organized compared to skeletal muscle fibers, with dyads instead of triads

    Smooth Muscle

    • Specialized for slow and steady contraction, under the influence of autonomic nerves and hormones
    • Found in blood vessels, digestive, respiratory, urinary, and reproductive tracts, and their associated organs
    • Each smooth muscle cell is elongated, tapering, and unstriated, with a single central nucleus
    • Covered by external lamina and collagen fibers, with narrow ends lying adjacent to broad parts of neighboring cells
    • Cells are linked together by gap junctions
    • Surface has numerous plasmalemma invaginations (caveolae) containing ion channels that control Ca2+ release to initiate contraction
    • Sarcoplasmic reticulum is present, but T-tubules are absent
    • Actin and myosin filaments crisscross the sarcoplasm obliquely, with myosin filaments having a less regular arrangement and fewer cross-bridges than in striated muscle
    • Actin filaments are attached to dense bodies, which serve as points for transmitting contractile force within and between cells
    • Contraction is stimulated by autonomic nerves and hormones, with axons forming varicosities in close contact with smooth muscle fibers
    • Smooth muscle cells also synthesize collagen, elastin, and proteoglycans, and actively synthesize extracellular matrix (ECM)

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    Description

    Learn about the composition, characteristics, and functions of cardiac muscle cells, including their structure, size, and contraction properties.

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