Table of contents

1. Introduction to Anatomy & Physiology5h 43m
2. Cell Chemistry & Cell Components12h 36m
3. Energy & Cell Processes10h 6m
4. Tissues & Histology10h 3m
5. Integumentary System2h 20m
6. Bones & Skeletal Tissue2h 16m
7. The Skeletal System2h 35m
8. Joints2h 17m
9. Muscle Tissue2h 33m
10. Muscles1h 11m
11. Nervous Tissue and Nervous System1h 35m
12. The Central Nervous System1h 6m
- Introduction to the Central Nervous System
  18m
- The Cerebrum
  48m
13. The Peripheral Nervous System1h 26m
14. The Autonomic Nervous System1h 38m
15. The Special Senses2h 41m
16. The Endocrine System2h 48m
17. The Blood3h 22m
18. The Heart3h 42m
19. The Blood Vessels3h 35m
20. The Lymphatic System3h 16m
21. The Immune System14h 37m
22. The Respiratory System3h 20m
23. The Digestive System2h 5m
24. Metabolism and Nutrition4h 0m
25. The Urinary System2h 39m
26. Fluid and Electrolyte Balance, Acid Base Balance37m
27. The Reproductive System2h 5m
28. Human Development1h 21m
29. Heredity3h 32m

18. The Heart

Electrical Conduction System of the Heart

Anatomy & Physiology

18. The Heart

Electrical Conduction System of the Heart

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Problem 18

Textbook Question

The cells of the conducting system differ from the contractile cells of the heart in that:
(a) Conducting cells are larger and contain more myofibrils
(b) Contractile cells exhibit pacemaker potentials
(c) Contractile cells do not normally exhibit autorhythmicity
(d) Both a and b are correct

Verified step by step guidance

Understand the difference between conducting cells and contractile cells in the heart. Conducting cells are specialized for initiating and propagating electrical signals, while contractile cells are responsible for the mechanical contraction of the heart.

Recall that conducting cells are part of the heart's intrinsic conduction system, including structures like the sinoatrial (SA) node, atrioventricular (AV) node, bundle branches, and Purkinje fibers. These cells exhibit autorhythmicity, meaning they can generate action potentials without external stimulation.

Note that contractile cells, which make up the majority of the myocardium, do not normally exhibit autorhythmicity. They rely on electrical signals from conducting cells to initiate contraction.

Evaluate the options provided in the problem: (a) Conducting cells are larger and contain more myofibrils—this is incorrect because conducting cells are smaller and contain fewer myofibrils compared to contractile cells. (b) Contractile cells exhibit pacemaker potentials—this is incorrect because pacemaker potentials are a feature of conducting cells, not contractile cells. (c) Contractile cells do not normally exhibit autorhythmicity—this is correct based on the physiological role of contractile cells.

Conclude that the correct answer is (c), as it accurately describes the lack of autorhythmicity in contractile cells, distinguishing them from conducting cells.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Conducting System of the Heart

The conducting system of the heart consists of specialized cells that generate and propagate electrical impulses, coordinating the heartbeat. Key components include the sinoatrial (SA) node, atrioventricular (AV) node, and Purkinje fibers. Unlike contractile cells, conducting cells are primarily responsible for initiating and conducting electrical signals rather than contracting.

Contractile Cells

Contractile cells, or cardiomyocytes, are the muscle cells of the heart responsible for contraction and pumping blood. They contain numerous myofibrils, which are essential for generating force. These cells typically do not have pacemaker potentials and rely on signals from the conducting system to initiate contraction.

Autorhythmicity

Autorhythmicity refers to the ability of certain cardiac cells to generate spontaneous action potentials without external stimuli. This property is primarily seen in the conducting cells of the heart, allowing them to set the rhythm of the heartbeat. In contrast, contractile cells do not exhibit this characteristic and depend on the conducting system for rhythmic contractions.