Questions and Answers
Which of the following are characteristics of cardiac muscle? (Select all that apply)
What occurs during ventricular systole? (Select all that apply)
How are the heart chambers involved in pulmonary circulation? (Select all that apply)
The resting membrane potential of cardiac muscle cells depends on a low permeability of the plasma membrane to sodium and potassium and a higher permeability to calcium.
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Action potentials in cardiac muscle last longer than those in skeletal muscle.
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In skeletal muscle there is a plateau phase, a period of slow repolarization, that is not found in cardiac muscle.
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What are the individual ion contributions to the resting membrane potential (RMP) of the SA nodal cells? (Select all that apply)
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SA nodal cells are unique in that they exhibit autorhythmicity, meaning they are capable of depolarizing and firing an action potential spontaneously without any external influence.
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What are the series of events in the SA nodal cells that directly cause autorhythmic contraction of cardiac muscle cells? (Select all that apply)
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What is the correct order of mechanical events associated with cardiac muscle contraction?
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The refractory period of skeletal muscle is longer than for cardiac muscle.
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Cardiac output (CO) is equivalent to heart rate (HR) multiplied by stroke volume (SV).
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What are the primary variables influencing stroke volume (SV)? (Select all that apply)
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Which are characteristics of the heart when it is at rest prior to atrial contraction (atrial systole)? (Select all that apply)
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What might happen if the fibrous skeleton was missing?
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Which are components of lymph? (Select all that apply)
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What is the function of the postcapillary venule?
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Study Notes
Cardiac Muscle Characteristics
- Cardiac muscle cells are short and branching, with one or two nuclei located centrally.
- Their structure includes thick and thin filaments, making them distinct from skeletal muscle.
- The contractile unit in cardiac muscle is the sarcomere.
Ventricular Systole Events
- During ventricular systole, semilunar valves open, allowing blood flow into the large arteries.
- The AV valves close to prevent backflow into the atria.
Heart Chambers in Pulmonary Circulation
- Oxygenated blood enters the left atrium from the lungs.
- The right ventricle is responsible for pumping deoxygenated blood to the lungs.
- Pulmonary veins carry oxygenated blood to the left atrium, while pulmonary arteries transport deoxygenated blood from the right ventricle.
Resting Membrane Potential in Cardiac Muscle
- The resting membrane potential of cardiac muscle cells does not rely on higher calcium permeability.
Action Potentials in Muscle Types
- Action potentials in cardiac muscle last significantly longer compared to those in skeletal muscle.
- Skeletal muscle does not exhibit a plateau phase, which is present in cardiac muscle.
SA Nodal Cell ion Contributions
- The resting membrane potential (RMP) of SA nodal cells is influenced by higher external sodium concentration, greater internal potassium concentration, and a calcium gradient with more calcium outside the cell.
Autorhythmicity of SA Nodal Cells
- SA nodal cells can depolarize and fire action potentials spontaneously due to their autorhythmic nature.
Events Leading to Autorhythmic Contraction
- Slow voltage-gated sodium channels open, initiating slow depolarization to threshold.
- Fast voltage-gated calcium channels further induce depolarization after threshold is reached.
- Voltage-gated potassium channels facilitate repolarization following contraction.
Mechanical Events of Cardiac Contraction
- Cardiac muscle contraction involves calcium entry into the sarcoplasm, binding to troponin, muscle contraction, and subsequent relaxation after calcium release from troponin.
Refractory Period Comparison
- The refractory period is shorter in cardiac muscle than in skeletal muscle.
Cardiac Output Calculation
- Cardiac output (CO) is calculated by multiplying heart rate (HR) by stroke volume (SV).
Stroke Volume Influencing Variables
- Key variables affecting stroke volume include afterload, venous return (preload), and contractility (inotropic agents).
Heart at Rest Prior to Atrial Systole
- During rest before atrial contraction, AV valves remain open, all chambers are at rest, and passive filling of the ventricles takes place.
Importance of the Fibrous Skeleton
- Absence of the fibrous skeleton would result in nearly simultaneous contraction of all four heart chambers.
Components of Lymph
- Lymph consists of interstitial fluid, solutes, and foreign material, playing essential roles in the body’s defense and fluid regulation.
Function of Postcapillary Venule
- The postcapillary venule's primary function is to drain the capillary bed, facilitating blood return.
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Test your knowledge of cardiac muscle characteristics and ventricular systole with this interactive flashcard quiz. Check all applicable answers to solidify your understanding of anatomy and physiology concepts.
