Control of Heartbeat (Heart Excitation & Contraction) — Easy Notes
1. Pacemaker (SA Node)
- Heartbeat starts from the SA node (Sinoatrial node –
natural pacemaker).
- It is a small cluster of cardiac muscle cells
(specialized auto-rhythmic cells).
- Located in the upper wall of the right atrium (right
upper chamber).
- It generates electrical impulses (tiny
bio-electrical signals) that make both atria contract
simultaneously (atria squeeze together).
2. AV Node (Atrioventricular Node)
- The impulse then reaches the AV node (relay station
between atria & ventricles).
- Located at the lower part of the interatrial septum
(wall between atria).
- AV node delays the impulse by 0.15 sec (pause
allowing atria to finish contraction).
3. Bundle of His (AV Bundle)
- From AV node, the impulse moves into the Bundle of
His (AV bundle – conducting fibre pathway).
- Present in the interventricular septum (wall between
ventricles).
- The bundle divides into right and left branches (two
pathways for ventricles).
4. Purkinje Fibres
- Branches end in Purkinje fibres (special fibres that
spread the impulse inside ventricles).
- These fibres cause both ventricles to contract
almost at the same time.
5. Why the 0.15 sec Delay?
- This delay between SA node & AV node
ensures:
- Atria complete systole (atrial contraction completed)
- Before ventricles begin systole (ventricular
contraction)
- This allows efficient filling of ventricles with
blood.
6. Artificial Pacemaker
- If impulses from the SA node are weak or blocked
(poor conduction) → heartbeat becomes irregular.
- Such patients receive an artificial pacemaker
(battery-operated device).
- It is implanted near the AV node (surgically placed
under skin).
- It emits electrical signals to maintain normal
rhythmic heartbeat.
Rate of Heartbeat — Easy Notes
1. Normal Heart Rate
- Adult heart beats about 70 times per minute.
- Pumps about 5 litres of blood per minute (entire
blood volume).
2. Pacemaker Control
- Normal heart rate is mainly controlled by:
- SA node (main pacemaker)
- AV node (secondary controller)
3. Brain Control
- Brain’s cardiac control centre (in medulla oblongata
– brainstem region) adjusts heart rate.
- During fever & exercise:
- Brain sends stimulating nerve signals (sympathetic
nerves)
- Heart rate increases to meet higher oxygen
demand.
- During rest or sleep:
- Brain sends inhibitory signals (parasympathetic
nerves)
- Heart rate slows down.
4. Daily Circulation Fact (for exam MCQs)
- About 8,000 litres of blood flow through 96,000
km of blood vessels every day.
MCQs on Control of Heartbeat & Heart Rate Regulation
1. The heartbeat is initiated by which structure?
A. AV node
B. Purkinje fibres
C. SA node
D. Bundle of His
Answer: C
Explanation: SA node is the natural pacemaker that starts the heartbeat.
2. Where is the SA node located?
A. Lower wall of left atrium
B. Upper wall of right atrium
C. Interventricular septum
D. Aortic arch
Answer: B
Explanation: SA node lies in the upper wall of the right atrium.
3. The SA node is composed of:
A. Nervous tissue
B. Skeletal muscle
C. Cardiac muscle cells
D. Smooth muscle cells
Answer: C
Explanation: It is a small cluster of specialized cardiac muscle cells.
4. What happens when the SA node fires electrical impulses?
A. Only ventricles contract
B. Only right atrium contracts
C. Both atria contract together
D. Both ventricles relax
Answer: C
Explanation: SA node causes simultaneous atrial contraction.
5. The AV node is located in:
A. Right atrium wall
B. Left atrium wall
C. Lower part of interatrial septum
D. Upper part of interventricular septum
Answer: C
Explanation: AV node lies in the lower part of the septum between atria.
6. The main function of the AV node is to:
A. Start the heartbeat
B. Delay the electrical impulse
C. Contract ventricles
D. Pump blood
Answer: B
Explanation: AV node delays impulse for 0.15 sec so atria finish systole.
7. The delay at the AV node lasts for:
A. 0.05 sec
B. 0.10 sec
C. 0.15 sec
D. 1 sec
Answer: C
Explanation: AV node slows conduction for about 0.15 seconds.
8. Why is the AV delay important?
A. Allows ventricles to relax
B. Allows atria to finish contraction
C. Reduces blood pressure
D. Increases heart size
Answer: B
Explanation: Delay ensures atrial systole completes before ventricular systole starts.
9. Bundle of His is present in:
A. Atrial wall
B. Interventricular septum
C. SA node
D. Aorta
Answer: B
Explanation: AV bundle runs through the interventricular septum.
10. Bundle of His divides into:
A. Two atrial branches
B. Three ventricular branches
C. Left and right bundle branches
D. Purkinje muscle fibres
Answer: C
Explanation: It splits into left and right branches heading to ventricles.
11. Purkinje fibres are located in:
A. SA node
B. Atrial walls
C. Ventricular walls
D. Aortic wall
Answer: C
Explanation: Purkinje fibres spread through ventricular walls.
12. Purkinje fibres cause:
A. Atrial contraction
B. Ventricular contraction
C. SA node firing
D. Blood oxygenation
Answer: B
Explanation: They stimulate ventricles to contract almost simultaneously.
13. If SA node fails, what happens?
A. No heartbeat
B. Irregular or slow heartbeat
C. Heart stops permanently
D. Blood pressure increases instantly
Answer: B
Explanation: Weak or blocked SA node causes delayed or irregular rhythm.
14. Artificial pacemaker is implanted near:
A. SA node
B. Aorta
C. AV node
D. Pulmonary artery
Answer: C
Explanation: It is placed near AV node to send electrical signals to the heart.
15. Artificial pacemaker works by:
A. Pumping blood
B. Sending electrical impulses
C. Expanding the arteries
D. Increasing blood pressure
Answer: B
Explanation: It replaces weak SA node by emitting electrical signals.
16. Normal adult heart rate is about:
A. 40 bpm
B. 70 bpm
C. 110 bpm
D. 150 bpm
Answer: B
17. An adult heart pumps about how much blood per minute?
A. 2 litres
B. 3 litres
C. 5 litres
D. 10 litres
Answer: C
Explanation: Approximately 5 litres are pumped every minute.
18. About how many litres of blood move daily through all vessels?
A. 1,000 L
B. 3,000 L
C. 8,000 L
D. 12,000 L
Answer: C
19. Total length of human blood vessels is about:
A. 1,000 km
B. 10,000 km
C. 50,000 km
D. 96,000 km
Answer: D
20. Heart rate increases during exercise due to:
A. Kidney hormones
B. Brain signals
C. Liver enzymes
D. Digestive activity
Answer: B
Explanation: Brain’s control centre sends sympathetic signals to increase rate.
21. During rest, which nerves slow the heart rate?
A. Sympathetic nerves
B. Motor nerves
C. Parasympathetic nerves
D. Sensory nerves
Answer: C
22. AV node acts as a:
A. Pump
B. Pacemaker
C. Relay centre
D. Blood filter
Answer: C
23. The SA node is also called the:
A. Secondary pacemaker
B. Natural pacemaker
C. Cardiac stabilizer
D. Cardiac inhibitor
Answer: B
24. Ventricular contraction begins when:
A. SA node fires
B. AV node delays impulse
C. Purkinje fibres are stimulated
D. Atria contract
Answer: C
25. Cardiac impulses travel in which order?
A. AV → SA → Purkinje → Bundle
B. SA → AV → Bundle → Purkinje
C. Bundle → SA → AV → Purkinje
D. SA → Purkinje → AV → Bundle
Answer: B
Explanation: Correct pathway of conduction.
26. The term “systole” refers to:
A. Relaxation
B. Contraction
C. Fibrillation
D. Repolarization
Answer: B
Explanation: Systole = contraction phase.
27. Weak SA node leads to:
A. Normal heartbeat
B. Fast heartbeat
C. Delayed/irregular heartbeat
D. Strong heartbeat
Answer: C
28. Which structure ensures ventricles contract together?
A. SA node
B. AV node
C. Purkinje fibres
D. Atria
Answer: C
29. The brain increases heart rate using:
A. Parasympathetic nerves
B. Sympathetic nerves
C. Endocrine glands
D. Reflex arcs
Answer: B
30. Heartbeat rhythmicity mainly depends on:
A. Lungs
B. AV node
C. Pacemaker
D. Brain stem
Answer: C
Short Questions with Answers (Control of Heartbeat & Heart Rate Regulation)
1. What is the SA node?
Answer: SA node is the natural pacemaker made of specialized cardiac muscle cells that initiate the heartbeat.
2. Where is the SA node located?
Answer: In the upper wall of the right atrium.
3. What happens when the SA node sends impulses?
Answer: Both atria contract simultaneously.
4. What is the AV node?
Answer: A cluster of cardiac cells that receives impulses from SA node and delays them before passing to ventricles.
5. Where is the AV node found?
Answer: In the lower part of the interatrial septum.
6. Why does the AV node delay the impulse?
Answer: To allow atria to complete systole before ventricles start contraction.
7. How long is the AV node delay?
Answer: About 0.15 seconds.
8. What is the Bundle of His?
Answer: A bundle of conducting fibres in the interventricular septum that carries impulses to the ventricles.
9. Into how many branches does the Bundle of His divide?
Answer: Into right and left branches.
10. What are Purkinje fibres?
Answer: Specialized fibres in ventricular walls that cause rapid and coordinated ventricular contraction.
11. What happens if the SA node becomes weak?
Answer: Heartbeat becomes slow or irregular due to poor impulse initiation.
12. What is an artificial pacemaker?
Answer: A battery-operated device implanted near the AV node to produce electrical impulses for normal heartbeat.
13. Why is an artificial pacemaker used?
Answer: To correct weak, slow, or blocked natural electrical signals in the heart.
14. What is the normal heart rate of an adult?
Answer: About 70 beats per minute.
15. How much blood does the heart pump per minute?
Answer: Around 5 litres.
16. How many litres of blood pass daily through vessels?
Answer: About 8,000 litres.
17. What is the total length of human blood vessels?
Answer: Approximately 96,000 km.
18. Who controls the basic heart rhythm?
Answer: SA node (pacemaker) and AV node.
19. How does the brain increase heart rate?
Answer: By sending sympathetic nerve signals.
20. When does the brain slow down heart rate?
Answer: During rest or sleep through parasympathetic signals.
21. What ensures both ventricles contract at the same time?
Answer: Purkinje fibres.
22. Give the correct sequence of impulse conduction in the heart.
Answer: SA node → AV node → Bundle of His → Purkinje fibres.
23. What is systole?
Answer: The contraction phase of the heart.
24. What is diastole?
Answer: The relaxation phase of the heart.
25. Why is coordinated contraction of chambers important?
Answer: It ensures efficient blood pumping without backflow.
Long Questions (Without Answers)
1.
Describe in detail the pathway of electrical impulse conduction in the human heart, starting from the SA node and ending at the Purkinje fibres.
2.
Explain the structure, location and role of the SA node and AV node in controlling the heartbeat. Why is their coordination essential?
3.
Discuss the significance of the 0.15-second delay at the AV node. How does this delay help in efficient functioning of the heart?
4.
Describe the Bundle of His and Purkinje fibres. Explain their role in ensuring coordinated ventricular contraction.
5.
Explain how an artificial pacemaker works, why it is used, and in which conditions it becomes necessary for heart patients.
6.
Describe the factors that regulate the rate of heartbeat in humans. Include the role of the pacemaker, AV node, and the brain’s control centre.
7.
Explain how the brain influences heart rate during exercise, fever, rest and sleep through the autonomic nervous system.
8.
Describe the conduction system of the heart with reference to its structures, functions, and importance in maintaining rhythmic heartbeat.
9.
Discuss the consequences of a blocked or weakened SA node. How does this affect cardiac rhythmicity?
10.
Write a detailed note on the initiation, regulation, and coordination of heart contraction in humans.
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