The Cardiovascular System (Heart) (Latest 2025 /
2026) Questions & Answers 100% Verified New
Brand
What is the relative refractory period of a cardiac muscle cell?
It occurs when Na+ channels are closed but can open if given a stronger than normal stimulus.
How long do cardiac action potentials last?
250-300 msec.
Why do cardiac action potentials last longer than action potentials in skeletal muscle?
Mainly due to the plateau phase.
What percentage of necessary Ca2+ for contraction is provided by Ca2+ ions entering the cell in a
cardiac muscle cell?
About 20%.
What triggers the release of additional Ca2+ from the sarcoplasmic reticulum in a cardiac muscle cell?
The entry of Ca2+ ions into the cell.
What does the release of additional Ca2+ from the sarcoplasmic reticulum during the plateau phase of
a cardiac muscle cell action potential result in?
A longer contraction.
How long do Ca2+ channels remain open during the plateau phase of a cardiac muscle cell action
potential?
175 msec.
When do sarcoplasmic Ca2+ levels remain elevated until in a cardiac muscle cell?
After the plateau phase.
What is the refractory period in cardiac muscle?
Lasts until after contraction has finished and relaxation is beginning.
What is the refractory period in skeletal muscle?
Ends before peak tension develops.
Can summation occur in cardiac muscle?
No, it is impossible due to the refractory period.
, What are the components of the heart's conduction system?
SA node, AV node, Bundle of His, Purkinje fibers
How does the heart's conduction system function?
SA node initiates electrical impulses, AV node delays impulses, Bundle of His and Purkinje fibers
distribute impulses
What does the P wave correspond to?
Depolarization of the atria
When does contraction begin after the start of the P wave?
100 msec after the start of the P wave
What does the QRS complex correspond to?
Ventricular depolarization
What does the QRS complex also include?
Repolarization of the atria
When do the ventricles contract?
After the peak of the R wave
What does the T wave represent?
Ventricular repolarization
What does the ECG record?
Electrical activity of the entire heart
What does the ECG show?
Depolarization that stimulates contraction
How is the ECG analyzed clinically?
By looking at size of voltage changes and determining the relative length and strength of the
waves
What can a large QRS complex indicate?
Enlarged heart, particularly ventricle
What can a small electrical signal on the ECG indicate?
Damage to heart muscle or electrical system, or bad monitoring
What does the P-R interval show?
2026) Questions & Answers 100% Verified New
Brand
What is the relative refractory period of a cardiac muscle cell?
It occurs when Na+ channels are closed but can open if given a stronger than normal stimulus.
How long do cardiac action potentials last?
250-300 msec.
Why do cardiac action potentials last longer than action potentials in skeletal muscle?
Mainly due to the plateau phase.
What percentage of necessary Ca2+ for contraction is provided by Ca2+ ions entering the cell in a
cardiac muscle cell?
About 20%.
What triggers the release of additional Ca2+ from the sarcoplasmic reticulum in a cardiac muscle cell?
The entry of Ca2+ ions into the cell.
What does the release of additional Ca2+ from the sarcoplasmic reticulum during the plateau phase of
a cardiac muscle cell action potential result in?
A longer contraction.
How long do Ca2+ channels remain open during the plateau phase of a cardiac muscle cell action
potential?
175 msec.
When do sarcoplasmic Ca2+ levels remain elevated until in a cardiac muscle cell?
After the plateau phase.
What is the refractory period in cardiac muscle?
Lasts until after contraction has finished and relaxation is beginning.
What is the refractory period in skeletal muscle?
Ends before peak tension develops.
Can summation occur in cardiac muscle?
No, it is impossible due to the refractory period.
, What are the components of the heart's conduction system?
SA node, AV node, Bundle of His, Purkinje fibers
How does the heart's conduction system function?
SA node initiates electrical impulses, AV node delays impulses, Bundle of His and Purkinje fibers
distribute impulses
What does the P wave correspond to?
Depolarization of the atria
When does contraction begin after the start of the P wave?
100 msec after the start of the P wave
What does the QRS complex correspond to?
Ventricular depolarization
What does the QRS complex also include?
Repolarization of the atria
When do the ventricles contract?
After the peak of the R wave
What does the T wave represent?
Ventricular repolarization
What does the ECG record?
Electrical activity of the entire heart
What does the ECG show?
Depolarization that stimulates contraction
How is the ECG analyzed clinically?
By looking at size of voltage changes and determining the relative length and strength of the
waves
What can a large QRS complex indicate?
Enlarged heart, particularly ventricle
What can a small electrical signal on the ECG indicate?
Damage to heart muscle or electrical system, or bad monitoring
What does the P-R interval show?
