40 Questions
What effect does marked hyperkalemia have on the heart?
Stops the heart in diastole
What is the main purpose of using digitalis in heart failure treatment?
Increase contractility
What does end diastolic volume refer to?
Volume of blood in each ventricle at the end of diastole
Which term is used to describe the ability of cardiac muscle to convert electrical and chemical changes into mechanical work?
Inotropism
What is the effect of +ve inotropic activity on contractility?
Increase contractility
What determines the initial length of the cardiac muscle?
Preload
What is the volume of blood that remains in each ventricle at the end of systole?
'End systolic volume'
What is the term for the amount of blood ejected by each ventricle per stroke?
'Stroke volume'
What is the primary function of the cardiac muscle's automaticity?
To allow the heart to beat regularly without nerve supply
What is the main factor that contributes to the cardiac muscle's automaticity?
Resting membrane potential
Which of the following cardiac muscle tissues has the highest inherent rhythmicity?
Sinoatrial node (SA node)
What is the main mechanism by which the SA node maintains its role as the primary cardiac pacemaker?
Steeper slope of diastolic depolarization
Which of the following factors can increase the heart's rhythmicity or chronotropism?
Increased sympathetic nervous activity
What is the main consequence of the cardiac muscle's rhythmicity or automaticity?
Regular and coordinated beating of the heart
Which of the following cardiac muscle properties is directly responsible for the heart's ability to conduct electrical impulses?
Conductivity
How does the cardiac muscle's contractility differ from its rhythmicity?
Contractility is a measure of force generation, while rhythmicity is a measure of beating rate
Which part of the cardiac conduction system is responsible for initiating the heartbeat?
SA node
Which part of the cardiac conduction system is responsible for transmitting the electrical impulse from the atria to the ventricles?
AV node
Which part of the cardiac conduction system is responsible for rapidly distributing the electrical impulse throughout the ventricles?
Purkinje fibers
What is the function of the bundle of His in the cardiac conduction system?
Coordinating the contraction of the atria and ventricles
Which part of the cardiac conduction system is responsible for the automaticity of the heart?
SA node
Which part of the cardiac conduction system is responsible for the electrical potentials of the pacemaker tissues?
SA node
Which part of the cardiac conduction system is responsible for the electrical potentials of the cardiac muscle fibers?
Purkinje fibers
Which part of the cardiac conduction system is responsible for the rhythmicity of the heart?
SA node
What is the effect of greater initial length of cardiac muscle fiber (End diastolic volume, EDV) on the force of contraction?
It increases the force of contraction.
What does afterload refer to in the context of heart function?
The resistance encountered by blood during ventricular ejection.
What happens to the initial velocity of shortening of cardiac muscle when afterload increases?
It decreases.
What does contractility refer to in the context of heart function?
Ability of the heart to expel blood independent of preload or afterload.
What phenomenon describes gradual increases in strength of cardiac muscle contraction due to repeated stimulation (increase in heart rate)?
Staircase (Treppe) phenomenon
What effect does sympathetic nervous system stimulation have on cardiac muscle contraction?
+ve inotropic effect
Which physical factor has a positive inotropic effect on cardiac muscle contraction?
Fever
Which chemical substance has a positive inotropic effect on cardiac muscle contraction?
Digitalis
What is the duration of the relative refractory period (RRP) in cardiac muscle?
0.05 seconds (50 milliseconds)
What is the significance of the refractory period in cardiac muscle?
It prevents stimulation of the ventricles by another impulse, allowing time for emptying and refilling.
When does the contraction of cardiac muscle (systole) reach its maximum?
At the end of the plateau phase
When does the relaxation of cardiac muscle (diastole) start?
During the rapid repolarization phase
Which nervous system component has a negative chronotropic effect on the heart, decreasing the heart rate?
Parasympathetic nervous system
What is the effect of warming (fever) on the heart rate?
Increases heart rate (positive chronotropic effect)
Which of the following ions, when increased, can decrease the heart rate?
All of the above
Which of the following conditions or substances can decrease the heart rate?
Digitalis
Test your knowledge on the automaticity, conducting system, excitation sequence, electrical potentials, factors affecting rhythmicity, and contractility of cardiac muscle. Learn about the properties of pacemaker tissues and cardiac muscle fibers.
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