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Questions and Answers
What is a key structural feature that distinguishes cardiac muscle cells from skeletal muscle cells?
What is a key structural feature that distinguishes cardiac muscle cells from skeletal muscle cells?
Which type of cells in cardiac muscle are responsible for initiating contractions?
Which type of cells in cardiac muscle are responsible for initiating contractions?
What role do intercalated discs play in cardiac muscle function?
What role do intercalated discs play in cardiac muscle function?
Which statement best describes the mitochondria in cardiac muscle cells?
Which statement best describes the mitochondria in cardiac muscle cells?
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What is the primary function of the myocardium?
What is the primary function of the myocardium?
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Which physiological feature is unique to cardiac muscle contraction?
Which physiological feature is unique to cardiac muscle contraction?
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How does the structure of T-tubules in cardiac muscle differ from those in skeletal muscle?
How does the structure of T-tubules in cardiac muscle differ from those in skeletal muscle?
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What effect do hormones have on cardiac muscle?
What effect do hormones have on cardiac muscle?
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Which event is responsible for the opening of Ryanodine receptors (RyR) in cardiac muscle?
Which event is responsible for the opening of Ryanodine receptors (RyR) in cardiac muscle?
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What mechanism is used to remove calcium from the cytoplasm during muscle relaxation in cardiac muscle?
What mechanism is used to remove calcium from the cytoplasm during muscle relaxation in cardiac muscle?
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What is a notable characteristic of the absolute refractory period in cardiac muscle action potentials?
What is a notable characteristic of the absolute refractory period in cardiac muscle action potentials?
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How does the contraction initiation in cardiac muscle primarily differ from that in skeletal muscle?
How does the contraction initiation in cardiac muscle primarily differ from that in skeletal muscle?
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Which type of muscle exhibits multinucleate fibers?
Which type of muscle exhibits multinucleate fibers?
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Which type of muscle is classified as having a graded contraction force for a single fiber twitch?
Which type of muscle is classified as having a graded contraction force for a single fiber twitch?
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What is the primary control mechanism for contraction in smooth muscle?
What is the primary control mechanism for contraction in smooth muscle?
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Which characteristic distinguishes cardiac muscle from skeletal and smooth muscle?
Which characteristic distinguishes cardiac muscle from skeletal and smooth muscle?
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Which muscle type is typically the slowest in contraction speed?
Which muscle type is typically the slowest in contraction speed?
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Where is cardiac muscle primarily located?
Where is cardiac muscle primarily located?
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Study Notes
Cardiac Muscle Overview
- Cardiac muscle shares characteristics with both skeletal and smooth muscle.
- It displays striations, formed by myosin and actin filaments arranged in sarcomeres.
- Contraction is via sliding thin filaments.
- Fibers are short, branched, and interconnected by intercalated discs with gap junctions.
Cardiac Muscle Cells
- Autorhythmic cells (pacemakers) initiate contractions, smaller than contractile cells, lacking organized sarcomeres, signal for contraction.
- Contractile cells display striated fibers, organized into sarcomeres, smaller than skeletal muscle fibers, have a single nucleus per fiber.
- Intercalated discs connect adjacent cells, forming a network allowing rapid transmission of electrical signals.
- Gap junctions facilitate rapid electrical signal transmission between cells.
- T-tubules in cardiac cells are larger and branch.
- Sarcoplasmic reticulum (SR) in cardiac muscle is smaller.
- Cardiac mitochondria occupy one-third of the cell volume.
Myocardium
- A myocardium is a mass of interconnected cardiac muscle cells.
- Myocardium acts as a single functional unit (similar to single-unit smooth muscle).
- Atria form one myocardium, and ventricles form another myocardium.
- Action potentials generated in any cardiac cell spread quickly through the myocardium.
Pacemaker Potential
- Cardiac muscle can produce action potentials automatically, without innervation (self-excitation).
- Heart rate is regulated by autonomic innervation and hormones.
- Action potential generation begins in the pacemaker region.
Excitation-Contraction Coupling in Cardiac Muscle
- Action potential from adjacent cells triggers voltage-gated calcium channels (DHPRs).
- Calcium (Ca2+) influx triggers a calcium spark.
- Sparks sum to generate a calcium signal.
- Calcium binds to troponin, initiating contraction. (Mechanism different to skeletal muscle).
- Calcium is pumped back into the sarcoplasmic reticulum for storage, and exchanged with sodium by NCX.
- Relaxation occurs when calcium unbinds from troponin.
Calcium Entry and Cardiac EC Coupling
- Action potential in cardiac muscle starts with pacemaker cells.
- Ca2+ induced Ca2+ release is different from skeletal muscle.
- Voltage-gated L-type calcium channels (DHPRs) open in the cell membrane.
- Ryanodine receptors (RyRs) open in the sarcoplasmic reticulum.
- Calcium sparks are summed to create a Calcium signal.
- Calcium binds to troponin initiating contraction.
- Cross-bridge cycle is similar to skeletal muscle.
- Relaxation removal of calcium from cytoplasm into SR with Ca2+-ATPase pump.
- Sodium-calcium exchanger (NCX) removes calcium from the cell.
Action Potentials: Skeletal vs. Cardiac Muscle
- Cardiac muscle action potentials have a longer absolute refractory period (~250 ms) preventing tetanic contractions that would interfere with the heart's pumping ability.
- Sk muscle APs are much faster, allowing for tetanic contractions.
Duration of Muscle Contraction
- Cardiac muscle contraction duration is intermediate between skeletal and smooth muscle contractions.
Comparison of Muscle Types
- Tables summarizing comparisons of skeletal, smooth, and cardiac muscle in terms of appearance, fiber arrangement, tissue morphology, internal structure, fiber proteins, control, contraction speed, and fiber twitch.
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Description
Explore the unique features of cardiac muscle, which combines aspects of both skeletal and smooth muscle. Understand the structure and function of cardiac muscle cells, including pacemaker cells and contractile fibers. This quiz will also cover the interconnections facilitated by intercalated discs and gap junctions.
