- 1(current)
Q. No.Assertion (A): SA-node is called pacemaker.
Reason (R): SA node generates least number of action potentials to initiate rhythmic contraction of heart.
1. Both (A) and (R) are true and (R) is the correct explanation of (A).
2. Both (A) and (R) are true but (R) is not the correct explanation of (A).
3. (A) is true but (R) is false.
4. Both (A) and (R) are false.
Reason (R): SA node generates least number of action potentials to initiate rhythmic contraction of heart.
1. Both (A) and (R) are true and (R) is the correct explanation of (A).
2. Both (A) and (R) are true but (R) is not the correct explanation of (A).
3. (A) is true but (R) is false.
4. Both (A) and (R) are false.
Subtopic: Â Human Heart: Gross Anatomy |Â Rhythmic Excitation of Human Heart: Part 1 |Â Rhythmic Excitation of Human Heart: Part 2 |
 88%
From NCERT
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Assertion (A): The cardiac impulse which originates from SA node in human heart cannot spread directly from atria to ventricles.
Reason (R): In human heart there is no continuity between cardiac muscle fibres of atria and those of ventricles except AV bundles.
1. Both (A) and (R) are true and (R) is the correct explanation of (A).
2. Both (A) and (R) are true but (R) is not the correct explanation of (A).
3. (A) is true but (R) is false.
4. Both (A) and (R) are false.
Reason (R): In human heart there is no continuity between cardiac muscle fibres of atria and those of ventricles except AV bundles.
1. Both (A) and (R) are true and (R) is the correct explanation of (A).
2. Both (A) and (R) are true but (R) is not the correct explanation of (A).
3. (A) is true but (R) is false.
4. Both (A) and (R) are false.
Subtopic: Â Human Heart: Cardiac Cycle |Â Rhythmic Excitation of Human Heart: Part 1 |Â Rhythmic Excitation of Human Heart: Part 2 |
 51%
From NCERT
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What prevents the atria and the ventricles from contracting at the same time?
1. Pacemaker cells located in the atria fire before the pacemaker cells in the ventricles.
2. It takes time for epinephrine to diffuse from the atria to the ventricles to trigger contraction
3. The electrical signal generated in the right atrium is delayed at the AV node before passing to the ventricles.
4. The Na+ channels responsible for initiating ventricular contraction are inactivated and need to return to activated configuration to the electrically stimulated.
1. Pacemaker cells located in the atria fire before the pacemaker cells in the ventricles.
2. It takes time for epinephrine to diffuse from the atria to the ventricles to trigger contraction
3. The electrical signal generated in the right atrium is delayed at the AV node before passing to the ventricles.
4. The Na+ channels responsible for initiating ventricular contraction are inactivated and need to return to activated configuration to the electrically stimulated.
Subtopic: Â Human Heart: Gross Anatomy |Â Human Heart: Cardiac Cycle |Â Rhythmic Excitation of Human Heart: Part 1 |Â Rhythmic Excitation of Human Heart: Part 2 |
 77%
From NCERT
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Q. No.
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