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Body Fluids and Circulation

Cardiac Conduction System Practice Questions

20 free Cardiac Conduction System practice questions for the NCERT Biology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.

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Question 1 of 20 Medium

Which structure acts as the primary pacemaker of the human heart?

  1. A Atrioventricular (AV) node
  2. B Purkinje fibres
  3. C Sinoatrial (SA) node
  4. D Bundle of His

Correct answer: Sinoatrial (SA) node

The sinoatrial (SA) node initiates electrical impulses that set the basic rhythm of the heart. It has the highest intrinsic rate of spontaneous depolarisation among all cardiac tissues, so it functions as the primary pacemaker.

Question 2 of 20 Medium

The SA node is located in which part of the heart?

  1. A Left atrium, near the pulmonary vein openings
  2. B Right atrium, near the superior vena cava
  3. C Interventricular septum, midway down
  4. D Apex of the left ventricle, beneath pericardium

Correct answer: Right atrium, near the superior vena cava

The SA node is situated in the right atrial wall near the opening of the superior vena cava. This location allows rapid spread of impulses across the atrial musculature to trigger coordinated atrial contraction.

Question 3 of 20 Medium

Which node receives impulses from the SA node and delays them before ventricular contraction?

  1. A SA node
  2. B Purkinje fibres
  3. C Atrioventricular (AV) node
  4. D Bundle branches and fibres

Correct answer: Atrioventricular (AV) node

The atrioventricular (AV) node delays impulse conduction by about 100 ms. This ensures the atria complete their contraction and fully empty into the ventricles before ventricular contraction begins.

Question 4 of 20 Medium

The main functional significance of AV nodal delay is to:

  1. A Prevent premature atrial contraction entirely
  2. B Allow the ventricles to fill with blood
  3. C Increase overall resting heart rate
  4. D Synchronise the timing of ventricular relaxation

Correct answer: Allow the ventricles to fill with blood

AV nodal delay allows sufficient time for the ventricles to fill with blood from the atria before ventricular contraction begins. This mechanical sequence improves cardiac output efficiency.

Question 5 of 20 Medium

Which part of the conduction system connects the AV node to ventricular myocardium?

  1. A SA node
  2. B Purkinje fibers
  3. C Bundle of His
  4. D Chordae tendineae

Correct answer: Bundle of His

The bundle of His transmits impulses from the AV node to the ventricles. It ensures rapid conduction toward the ventricular muscle.

Question 6 of 20 Medium

Purkinje fibers primarily function to:

  1. A Generate the primary cardiac rhythm spontaneously
  2. B Delay conduction between atria and ventricles
  3. C Spread impulses across the ventricular walls
  4. D Prevent backflow of blood between chambers

Correct answer: Spread impulses across the ventricular walls

Purkinje fibres spread electrical impulses rapidly throughout the ventricular myocardium. This ensures coordinated, near-simultaneous ventricular contraction for efficient ejection of blood.

Question 7 of 20 Medium

If the SA node fails, which structure can take over as pacemaker at a slower rate?

  1. A AV node — 40 to 60 beats per minute
  2. B His bundle — 30 to 40 bpm
  3. C Purkinje fibres — 20 to 40 beats per minute
  4. D Ventricular muscle — 20 to 30 beats per minute

Correct answer: AV node — 40 to 60 beats per minute

The AV node can act as a secondary pacemaker if the SA node fails, generating impulses at 40–60 bpm. Lower-order sites such as the bundle of His and Purkinje fibres can also take over but at even slower intrinsic rates.

Question 8 of 20 Medium

The intrinsic rhythmicity of the heart is due to:

  1. A Autonomic nervous stimulation only
  2. B Hormonal regulation by catecholamines
  3. C Myogenic activity of nodal tissue
  4. D Mechanical stretch from venous return

Correct answer: Myogenic activity of nodal tissue

The heart shows myogenic rhythm due to specialised nodal tissue — primarily the SA node — that can generate impulses independently of any nervous input. Autonomic nerves only modulate the rate.

Question 9 of 20 Medium

Which cardiac tissue has the highest rate of spontaneous depolarization?

  1. A Atrioventricular (AV) node
  2. B Purkinje fibres
  3. C Sinoatrial (SA) node
  4. D Ventricular muscle

Correct answer: Sinoatrial (SA) node

SA node cells depolarise spontaneously at the fastest rate (60–80 bpm) of all cardiac tissues. This dominance allows the SA node to function as the primary pacemaker, overriding the slower intrinsic rates of other conduction tissues.

Question 10 of 20 Medium

The AV node is located at the junction of:

  1. A Atria and ventricles
  2. B Right and left atria
  3. C Right and left ventricles
  4. D Vena cava and atrium

Correct answer: Atria and ventricles

The AV node lies at the atrioventricular junction. This position allows it to regulate impulse transmission between atria and ventricles.

Question 11 of 20 Medium

Which structure ensures that impulses reach the apex of the heart first?

  1. A SA node
  2. B AV node
  3. C Bundle branches
  4. D Purkinje fibers

Correct answer: Purkinje fibers

Purkinje fibers extend to the apex of the ventricles. This ensures contraction starts at the apex and moves upward efficiently.

Question 12 of 20 Medium

Bundle branches are located in the:

  1. A Walls of both atria
  2. B Interatrial septum near SA node
  3. C Interventricular septum
  4. D Outer wall of left ventricle

Correct answer: Interventricular septum

The right and left bundle branches run along the interventricular septum. From there they fan out toward their respective ventricular walls to conduct impulses efficiently.

Question 13 of 20 Medium

Which event occurs first in the normal cardiac conduction sequence?

  1. A Ventricular contraction
  2. B Impulse generation in SA node
  3. C Impulse reaches Purkinje fibers
  4. D AV nodal delay

Correct answer: Impulse generation in SA node

The sequence begins with impulse generation in the SA node. This initiates the heartbeat and subsequent conduction events.

Question 14 of 20 Medium

Damage to the AV node would most directly affect:

  1. A Rate and force of atrial contraction
  2. B Impulse conduction to ventricles
  3. C Diastolic filling of the ventricles
  4. D Oxygenation of blood in the lungs

Correct answer: Impulse conduction to ventricles

The AV node is the sole electrical gateway between atria and ventricles. Damage impairs or blocks this pathway, disrupting ventricular activation and potentially causing heart block.

Question 15 of 20 Medium

Which structure prevents simultaneous contraction of atria and ventricles?

  1. A SA node pacing
  2. B Fibrous cardiac skeleton
  3. C Purkinje fibre distribution
  4. D Chordae tendineae attachments

Correct answer: Fibrous cardiac skeleton

The fibrous skeleton of the heart electrically insulates the atria from the ventricles. This ensures impulses must travel only through the AV node, preventing simultaneous contraction of both chambers.

Question 16 of 20 Medium

The rate of impulse generation in the SA node is normally about:

  1. A About 30–40 beats per minute
  2. B About 40–60 beats per minute
  3. C About 60–80 beats per minute
  4. D About 100–120 beats per minute

Correct answer: About 60–80 beats per minute

The SA node typically generates impulses 60–80 times per minute in resting adults. This determines the normal resting heart rate, sometimes called sinus rhythm.

Question 17 of 20 Medium

Which ion plays a major role in spontaneous depolarization of SA node cells?

  1. A Chloride
  2. B Potassium
  3. C Calcium ions
  4. D Sodium ions

Correct answer: Sodium ions

Slow inward sodium influx (the 'funny current') is the primary driver of spontaneous diastolic depolarisation in SA node pacemaker cells, gradually raising the membrane potential until the threshold for an action potential is reached.

Question 18 of 20 Medium

The conducting fibers with the fastest impulse transmission speed are:

  1. A Purkinje fibers
  2. B Bundle of His
  3. C AV nodal fibers
  4. D SA nodal fibers

Correct answer: Purkinje fibers

Purkinje fibers have the highest conduction velocity. This ensures rapid and coordinated ventricular contraction.

Question 19 of 20 Medium

Which statement correctly describes cardiac conduction?

  1. A It is entirely under voluntary control
  2. B It depends only on nervous stimulation
  3. C It is myogenic but modulated by nerves
  4. D It requires continuous hormone secretion

Correct answer: It is myogenic but modulated by nerves

Cardiac conduction is myogenic in origin. Autonomic nerves only modify the rate and force of contractions.

Question 20 of 20 Medium

Complete heart block is most likely due to failure of conduction at the:

  1. A SA node (sinoatrial node)
  2. B AV node (atrioventricular node)
  3. C Purkinje fibres throughout the ventricles
  4. D Ventricular muscle itself

Correct answer: AV node (atrioventricular node)

Complete heart block results from impaired conduction through the AV node, severing the electrical link between atria and ventricles. Consequently, the atria and ventricles beat independently at their respective intrinsic rates.

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