Podcast
Questions and Answers
The natural pacemaker of the heart is the ______ node.
The natural pacemaker of the heart is the ______ node.
Sinoatrial
Cardiac myocytes are interconnected by structures called ______ disks.
Cardiac myocytes are interconnected by structures called ______ disks.
intercalated
The ______ junctions in cardiac myocytes link cells electrically.
The ______ junctions in cardiac myocytes link cells electrically.
gap
Desmosomes connect intermediate filaments from two adjacent ______.
Desmosomes connect intermediate filaments from two adjacent ______.
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Cardiac contraction has an absolute requirement for ______ influx through L-type Ca 2+ channels.
Cardiac contraction has an absolute requirement for ______ influx through L-type Ca 2+ channels.
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The heart consists of a right heart that pumps blood through the ______.
The heart consists of a right heart that pumps blood through the ______.
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Each atrium acts as a weak primer pump for the ______.
Each atrium acts as a weak primer pump for the ______.
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The heart is composed of three major types of cardiac muscle: atrial muscle, ventricular muscle, and specialized ______ muscle fibers.
The heart is composed of three major types of cardiac muscle: atrial muscle, ventricular muscle, and specialized ______ muscle fibers.
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The duration of contraction in cardiac muscle is much longer than in ______ muscle.
The duration of contraction in cardiac muscle is much longer than in ______ muscle.
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The specialized fibers exhibit automatic rhythmical ______ discharge in the form of action potentials.
The specialized fibers exhibit automatic rhythmical ______ discharge in the form of action potentials.
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Gap junctions enable passive diffusion of various compounds, like metabolites, water, and ions, up to a molecular mass of ______ Daltons.
Gap junctions enable passive diffusion of various compounds, like metabolites, water, and ions, up to a molecular mass of ______ Daltons.
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A gap junction channel consists of twelve ______ proteins.
A gap junction channel consists of twelve ______ proteins.
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Adherens junctions are constructed from ______ and catenins.
Adherens junctions are constructed from ______ and catenins.
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At the adherens junctions, the opposing membranes become separated by approximately ______ nm.
At the adherens junctions, the opposing membranes become separated by approximately ______ nm.
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The action potential of cardiac muscle averages about ______ millivolts.
The action potential of cardiac muscle averages about ______ millivolts.
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During each heartbeat, the intracellular potential rises from about ______ millivolts to about +20 millivolts.
During each heartbeat, the intracellular potential rises from about ______ millivolts to about +20 millivolts.
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The plateau in the action potential of cardiac muscle is due to the opening of fast sodium channels and slow ______ channels.
The plateau in the action potential of cardiac muscle is due to the opening of fast sodium channels and slow ______ channels.
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The presence of a plateau in the action potential causes ventricular contraction to last as much as ______ times longer in cardiac muscle than in skeletal muscle.
The presence of a plateau in the action potential causes ventricular contraction to last as much as ______ times longer in cardiac muscle than in skeletal muscle.
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The action potential in skeletal muscle is primarily caused by opening of large numbers of fast ______ channels.
The action potential in skeletal muscle is primarily caused by opening of large numbers of fast ______ channels.
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The prolonged action potential and plateau in cardiac muscle are due to differences in membrane properties compared to ______ muscle.
The prolonged action potential and plateau in cardiac muscle are due to differences in membrane properties compared to ______ muscle.
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Study Notes
The Heart and its Disorders
- The heart is two separate pumps
- A right heart that pumps blood through the lungs
- A left heart that pumps blood through peripheral organs
- Each heart is a pulsatile two-chamber pump
- Composed of an atrium and a ventricle
- Atria are weak primer pumps for the ventricles
- Ventricles provide the main pumping force
- Blood flows through the pulmonary circulation (right ventricle)
- Blood flows through the peripheral circulation (left ventricle)
Learning Objectives
- Understanding heart tissue and its functions
- Cardiac cycle and ECG
- Disorders of the heart and treatments
Anatomy of the Heart
- Figure 9-1 shows a diagram of the heart's structure
- The structure includes the aorta, pulmonary artery, pulmonary vein, left atrium, mitral valve, aortic valve, left ventricle, superior vena cava, right atrium, pulmonary valve, and tricuspid valve, right ventricle, and inferior vena cava.
- Shows the course of blood flow through the heart's chambers and heart valves
Physiology of Cardiac Muscle
- The heart contains three major types of cardiac muscle: atrial, ventricular, and specialized excitatory/conductive muscle fibers.
- The specialized fibers control the heart's rhythmical beating
- Atrial and ventricular muscle contract similar to skeletal muscle, but contraction duration is longer.
- Specialized excitatory and conductive fibers contract weakly due to fewer contractile fibrils
- These fibers exhibit automatic rhythmical electrical discharges (action potentials) or conduct action potentials through the heart.
- This function helps the excitatory system of the heart control the rhythmical beating of the heart.
Cardiac Conductive Muscle Fibers
- The heart has a special system for rhythmical electrical impulses for contraction
- Conducts impulses rapidly to the heart's different parts.
- Key areas include the Sinoatrial (SA) node (pacemaker in right atrium), Atrioventricular (AV) node (junction between atria and ventricles), Bundle of His (conducts impulses from AV to ventricles), Purkinje fibers (spread throughout ventricles for coordinated contraction).
Cardiac Myocytes
- Cardiac myocytes are shorter, branched, interconnected cells
- Intercalated disks connect the cells, containing desmosomes (mechanical), adherens junctions (mechanical link to actin cytoskeleton), and gap junctions (electrical link)
- Cardiac muscle is striated, with similar thin and thick filaments like skeletal muscle.
- Calcium influx through L-type Ca2+ channels is crucial for cardiac contraction
Desmosomes
- Connect intermediate filaments from adjacent cardiomyocytes
- Formed by a dense protein complex in intercalated disks
- Major players: transmembrane cadherins (e.g., desmogleins, desmocollins), cytoplasmic anchors (e.g. plakophilins, plakoglobin), and cytoskeletal adaptors (e.g., desmoplakin)
Gap Junctions
- Essential for chemical and electrical coupling of neighboring cells
- Intercellular channels connecting cytoplasm
- Allow passive diffusion of compounds (up to ~1000 daltons) like metabolites, water, and ions.
- Formed from connexin proteins (12 total, 6 from each cell forming a hemi-channel, connexon)
Adherens Junctions
- Composed of cadherins and catenins
- Cadherins zip cells together (homophilic)
- Link to actin cytoskeleton via catenins
- Cell membranes become separated by 20 nm.
Action Potentials in Cardiac Muscle
- Ventricular muscle fiber action potential averages ~105 millivolts
- Initial spike followed by a plateau (~0.2 seconds) then repolarization.
- The plateau in the action potential extends ventricular contraction ~15 times longer than in skeletal muscle.
- Plateau is caused by the opening of both fast sodium channels and slow calcium (calcium-sodium) channels.
Velocity of Signal Conduction in Cardiac Muscle
- Velocity of signal conduction in atrial/ventricular muscle fibers is ~0.3-0.5 m/sec.
- Much slower than in large nerve fibers, (~1/250th) and skeletal muscle fibers (~1/10th)
- Purkinje fibers have a conduction velocity as high as 4m/sec, allowing for rapid conduction throughout the heart.
The Cardiac Cycle
- Events from one heartbeat to the next
- Initiated by spontaneous action potential generation in the sinus node
- Delay of more than 0.1 second for the cardiac impulse to travel from atria to the ventricles.
- The cardiac cycle has a period of relaxation (diastole) and contraction (systole) to fill with and pump blood.
Consequences of A-V Block
- With sudden A-V bundle block, the Purkinje system delay intrinsic rhythmical impulses for 5 to 20 seconds
- During this delay, the ventricles fail to pump blood, causing the person to faint.
- This delayed pickup is called Stokes-Adams syndrome
- Prolonged delay can cause death.
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Description
Test your knowledge on the key concepts of cardiac physiology. This quiz covers aspects like the heart's natural pacemaker, cardiac muscle types, and the role of ion channels in contraction. Perfect for students studying biology, physiology, or medicine.
