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Questions and Answers
What is the duration of the absolute refractory period in cardiac muscle?
What is the duration of the absolute refractory period in cardiac muscle?
How does cardiac muscle differ from skeletal muscle regarding force of contraction?
How does cardiac muscle differ from skeletal muscle regarding force of contraction?
What role do calcium ions play in cardiac muscle contraction?
What role do calcium ions play in cardiac muscle contraction?
What is the primary mechanism for increasing the force of contraction in cardiac muscle?
What is the primary mechanism for increasing the force of contraction in cardiac muscle?
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What occurs during the refractory period in cardiac muscle cells?
What occurs during the refractory period in cardiac muscle cells?
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What is the primary function of conducting cardiac muscle cells?
What is the primary function of conducting cardiac muscle cells?
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What is the role of intercalated discs in cardiac muscle?
What is the role of intercalated discs in cardiac muscle?
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How do contractile cardiac muscle cells primarily obtain energy?
How do contractile cardiac muscle cells primarily obtain energy?
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What distinguishes conducting cardiac muscle cells from contractile cardiac muscle cells?
What distinguishes conducting cardiac muscle cells from contractile cardiac muscle cells?
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What type of muscle fibers do contractile cardiac muscle cells primarily represent?
What type of muscle fibers do contractile cardiac muscle cells primarily represent?
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What characteristic of cardiac muscle cells prevents the occurrence of tetanus?
What characteristic of cardiac muscle cells prevents the occurrence of tetanus?
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Which component of intercalated discs allows cells to function as an electrical syncytium?
Which component of intercalated discs allows cells to function as an electrical syncytium?
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What is the main role of contractile cardiac muscle fibers?
What is the main role of contractile cardiac muscle fibers?
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What is the primary function of the plasma membrane CaATPase in cardiac muscle cells?
What is the primary function of the plasma membrane CaATPase in cardiac muscle cells?
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During which phase of the action potential are voltage gated Na+ channels inactivated?
During which phase of the action potential are voltage gated Na+ channels inactivated?
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What occurs during the plateau phase (Phase 2) of the cardiac action potential?
What occurs during the plateau phase (Phase 2) of the cardiac action potential?
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How does the duration of the action potential in cardiac muscle cells compare to that in skeletal muscle cells?
How does the duration of the action potential in cardiac muscle cells compare to that in skeletal muscle cells?
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What is the absolute refractory period in cardiac muscle cells primarily associated with?
What is the absolute refractory period in cardiac muscle cells primarily associated with?
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What triggers the opening of Ca++ gated Ca++ release channels during cardiac contractions?
What triggers the opening of Ca++ gated Ca++ release channels during cardiac contractions?
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What is the typical duration of a contraction (twitch) in cardiac muscle compared to the action potential?
What is the typical duration of a contraction (twitch) in cardiac muscle compared to the action potential?
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What is necessary for a second action potential to occur during the relative refractory period?
What is necessary for a second action potential to occur during the relative refractory period?
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What primarily restores the resting membrane potential in cardiac muscle cells after an action potential?
What primarily restores the resting membrane potential in cardiac muscle cells after an action potential?
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The voltage gated Na+ channels must change from which state to be able to reopen?
The voltage gated Na+ channels must change from which state to be able to reopen?
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What percentage of energy used by cardiac muscle primarily comes from fat?
What percentage of energy used by cardiac muscle primarily comes from fat?
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During which phase does the cardiac muscle receive blood supply?
During which phase does the cardiac muscle receive blood supply?
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Which type of cardiac muscle cell is responsible for the conduction system?
Which type of cardiac muscle cell is responsible for the conduction system?
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What ion plays a crucial role in the electrical-contraction coupling in cardiac muscle?
What ion plays a crucial role in the electrical-contraction coupling in cardiac muscle?
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What is the predominant type of metabolism utilized by cardiac muscle?
What is the predominant type of metabolism utilized by cardiac muscle?
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The conductive cardiac muscle cells differ from contractile cells in that they primarily:
The conductive cardiac muscle cells differ from contractile cells in that they primarily:
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Which characteristic describes the ability of cardiac muscle to generate rhythmic contractions without external stimuli?
Which characteristic describes the ability of cardiac muscle to generate rhythmic contractions without external stimuli?
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Which statement about oxygen consumption in cardiac muscle is true?
Which statement about oxygen consumption in cardiac muscle is true?
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What structure connects cardiac muscle fibers and facilitates communication between them?
What structure connects cardiac muscle fibers and facilitates communication between them?
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What occurs immediately after depolarization of the T tubule membrane in cardiac muscle cells?
What occurs immediately after depolarization of the T tubule membrane in cardiac muscle cells?
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Study Notes
Cardiac Muscle Structure and Function
- Cardiac muscle is a striated fiber with similar contractile filament arrangements as skeletal muscle.
- Intercalated discs connect muscle fibers end-to-end.
- These discs are specialized attachments, preventing cell separation, and consist of gap junctions.
- Gap junctions allow cells to act as an electrical syncytium, facilitating coordinated contractions.
- Cardiac muscle cells are a combination of conducting and contractile cells.
Types of Cardiac Muscle Cells
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Conducting cardiac muscle cells make up 1% of cardiac muscle cells.
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These cells are large and specialized for excitation, without producing tension.
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They form a network called the conduction system in the heart, connected by gap junctions to contractile cells.
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Conducting fibers primarily consist of glycogen and have few myofilaments.
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These cells are the heart's intrinsic pacemakers.
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Contractile cardiac muscle cells are slow oxidative muscle fibers, forming the heart walls.
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These cells shorten and produce tension, using glucose and fatty acids as substrates.
Characteristics of Cardiac Muscle
- Histology: Shows the striated appearance of cardiac muscle tissue.
- Functional syncytium: Enables integrated contraction.
- Source of energy: Predominantly fat (60%), carbohydrates (35%), with ketones and amino acids making up the remaining 5%.
- Blood flow: Occurs during diastole (relaxation phase) in the left ventricle, and during systole and diastole in the right ventricle.
- Oxygen consumption: High oxygen consumption primarily through aerobic metabolism;anaerobic metabolism contributes less than 1%.
- Metabolism: High oxygen demand characteristic of cardiac muscle.
- Automaticity: Heart's ability to generate its own rhythmic contractions.
- Rhythmicity: Contractions occur rhythmically without external stimuli, unlike skeletal muscles, due to the conducting fibers in the heart.
- Conductivity: The heart's ability to transmit electrical impulses throughout the muscle.
- Action potential: Electrochemical signals generating muscle contractions.
- Recruitment: Not a factor in cardiac muscle due to the syncytial action.
Electrical-Contraction Coupling
- Cardiac muscle contraction, similar to skeletal muscles, involves calcium ions entering the cell.
- Depolarization of T-tubules allows calcium influx.
- Calcium triggers calcium release from the sarcoplasmic reticulum.
- This calcium release initiates cross-bridge formation and muscle contraction.
- Calcium removal via CaATPase, ends the contractile cycle, and causes muscle relaxation.
- Additional mechanisms for calcium removal exist, such as the Na+-Ca2+ exchanger.
Action Potential of Cardiac Muscles
- Cardiac action potential is longer and differs from skeletal muscle.
- Four phases characterize the cardiac action potential: phase 0 (rapid depolarization), phase 1 (initial repolarization), phase 2 (plateau), and phase 3 (rapid repolarization).
- Phase 4: Maintains a stable resting membrane potential.
- Phase 0: The voltage-gated Na+ channels open rapidly, leading to a rapid depolarization of the membrane towards threshold.
- Phase 1: Brief repolarization.
- Phase 2 (Plateau): L-type voltage-gated calcium channels open, slowing repolarization and giving the plateau phase in the graph.
- Phase 3: Rapid repolarization.
- Phase 4: Return to stable resting membrane potential.
Refractory Period
- In cardiac muscle, the absolute refractory period (180 msec) is almost as long as the action potential, preventing tetanus (sustained muscle contraction).
- This prolonged refractory period is crucial for rhythmic pumping of blood to prevent heart failure.
Absence of Muscle Fiber Recruitment
- Contractile cardiac cells function via an electrical syncytium, making traditional fiber recruitment impossible.
- Other mechanisms increase heart contraction force without fiber recruitment, such as by increasing stretch (Frank-Starling law).
Key Concepts
- Cardiac muscle uses overlapping actin and myosin proteins, producing shortening and generating force.
- Calcium ion mediates the link between membrane action potentials and contraction.
- The autonomic nervous system and hormones also regulate cardiac muscle activity.
- The cardiac muscle length-tension relationship, is also known as the Frank-Starling mechanism, which further increases the cardiac output.
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Description
Explore the fascinating structure and function of cardiac muscle. This quiz delves into the different types of cardiac muscle cells, their unique properties, and how they work together to enable the heart's efficient operation. Test your knowledge on the conduction system and the role of muscular fibers in cardiac activity.
