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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?
What is the primary function of smooth muscle cells in the body?
Where are smooth muscle cells typically found in the body?
What is the shape of smooth muscle cells?
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What type of junctions connect smooth muscle cells together?
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What are the small invaginations of the plasmalemma in smooth muscle cells called?
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How do actin filaments differ between smooth muscle cells and striated muscle cells?
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What is the function of dense bodies in smooth muscle cells?
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What type of junctions allow smooth muscle cells to contract synchronously?
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What is the function of gap junctions in the intercalated disc?
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Which of the following hormones stimulates smooth muscle contraction in the uterus?
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What is the main difference in the structure of cardiac muscle cells compared to skeletal muscle cells?
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What type of muscle cells can supplement fibroblast activity by synthesizing collagen, elastin, and proteoglycans?
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What is the primary function of varicosities in autonomic nerves?
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What is the primary source of energy for cardiac muscle cells?
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What is the function of desmosomes in the intercalated disc?
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Which of the following is NOT a characteristic of smooth muscle?
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What is the main difference between the ventricular and atrial T-tubules?
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What type of filaments are composed of desmin and attach to dense bodies in smooth muscle cells?
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What is the percentage of cell volume occupied by mitochondria in cardiac muscle cells?
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What is the characteristic of cardiac muscle contraction compared to skeletal muscle contraction?
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What is the characteristic of the sarcoplasmic reticulum in cardiac muscle cells compared to skeletal muscle cells?
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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.
