WorksheetsElectrical and Mechanical Properties of Cardiac Muscle
Total questions: 22
Worksheet time: 7mins
What does “excitability” mean in cardiac muscle?
Ability to contract
Ability to respond to a stimulus by forming a wave of depolarization
Ability to pump blood
Ability to relax
The electrical events generated by cardiac muscle with each heartbeat are recorded as
Electrocardiogram (ECG)
Electromyogram (EMG)
Electroencephalogram (EEG)
Echocardiogram
Which phase of the cardiac muscle action potential is known as the depolarization phase?
Phase 0
Phase 1
Phase 2
Phase 3
Phase 4
Which ion mainly enters the cell during the plateau phase of the cardiac action potential?
Sodium (Na⁺)
Potassium (K⁺)
Calcium (Ca²⁺)
Chloride (Cl⁻)
Autorhythmicity means
The ability to contract only when stimulated
The ability to respond to hormones
The ability to relax after contraction
The ability to generate impulses spontaneously
Pacemaker potential is also called
Plateau potential
Pre-potential or diastolic potential
Threshold potential
Resting potential
Which of the following are pacemaker tissues?
SA node
AV node
Bundle of His (AV bundle)
Purkinje fibers
Why does the SA node control the heart’s rhythm rather than the AV node?
AV node has stronger contraction
SA node has a plateau phase
SA node discharges at the fastest rate
AV node is more excitable
Which property of cardiac muscle allows impulses to travel through the heart?
excitability
elasticity
contractility
conductivity
Impulse conduction speed is slowest in the
SA node
AV node
Purkinje fibers
Ventricular muscle
Impulse conduction velocity is fastest in the
Atrial muscle
AV node
SA node
Purkinje fibers
Time delay at the AV node is important because it allows
Atria to contract before ventricles
Ventricles to contract before atria
Blood to flow backward
Impulse to stop in the AV node
Which bundle begins to conduct before the other due to wall thickness differences?
Left bundle branch
Right bundle branch
Both simultaneously
Septal bundle
Contractility means
The ability of cardiac muscle to contract after excitation
The ability to conduct impulses
The ability to generate impulses
The ability to resist stretching
Excitation–contraction coupling in cardiac muscle involves
Calcium influx through T-tubules
Calcium release from sarcoplasmic reticulum
Sodium efflux
Potassium accumulation
Which ion binds to troponin to initiate contraction?
Sodium (Na⁺)
Calcium (Ca²⁺)
Potassium (K⁺)
Magnesium (Mg²⁺)
Which phase of the cardiac action potential corresponds to the plateau?
Phase 0
Phase 1
Phase 2
Phase 3
Phase 4
Compared with skeletal muscle, cardiac muscle action potential duration is
longer
shorter
equal
absent
The “all-or-none law” means
A weak stimulus produces a weak contraction
A strong stimulus produces a stronger contraction
Once threshold is reached, a full action potential is generated
Action potential amplitude depends on stimulus strength
The relative refractory period occurs during
Depolarization
Plateau
Late repolarization
Resting phase
During the relative refractory period
Only stronger-than-normal stimuli can excite the muscle
No stimulus can excite the muscle
All sodium channels are inactivated
The heart is in systole
During excitation–contraction coupling, Ca²⁺ enters mainly from
Mitochondria
Cytoplasm
Lysosomes
Extracellular fluid via T-tubules
