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

Cardiac Action Potentials

Anatomy & Physiology

18. The Heart

Cardiac Action Potentials

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Problem 9

Textbook Question

What are the effects of the plateau phase of the contractile cell action potential?

Verified step by step guidance

Understand that the plateau phase is a unique feature of the action potential in cardiac contractile cells, which distinguishes it from the action potentials in skeletal muscle or neurons.

Recognize that the plateau phase is caused by the simultaneous influx of calcium ions (Ca²⁺) through voltage-gated calcium channels and the efflux of potassium ions (K⁺) through potassium channels. This balance maintains a prolonged depolarization.

Explain that the prolonged depolarization during the plateau phase ensures a longer contraction period for cardiac muscle cells, which is critical for effective blood pumping by the heart.

Discuss how the plateau phase prevents tetany (sustained contraction) in cardiac muscle by extending the refractory period, ensuring that the heart muscle relaxes between beats to allow proper filling of the chambers.

Highlight the importance of calcium ion influx during the plateau phase, as it triggers calcium-induced calcium release from the sarcoplasmic reticulum, which is essential for the contraction of cardiac muscle cells.

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Key Concepts

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

Plateau Phase

The plateau phase is a unique part of the cardiac action potential, particularly in contractile cells, characterized by a prolonged depolarization. This phase occurs after the initial rapid depolarization and is primarily maintained by the influx of calcium ions through L-type calcium channels. It plays a crucial role in ensuring that the heart muscle contracts effectively and prevents tetany, allowing for a coordinated heartbeat.

Calcium Ions in Cardiac Function

Calcium ions are essential for muscle contraction in cardiac cells. During the plateau phase, the influx of calcium not only sustains depolarization but also triggers the release of more calcium from the sarcoplasmic reticulum, leading to muscle contraction. This calcium-induced calcium release is vital for the strength and duration of the cardiac contraction, influencing overall heart function.

Refractory Period

The refractory period is the time during which a cardiac cell cannot be re-excited after an action potential. The plateau phase contributes to a longer refractory period, which is crucial for preventing arrhythmias by ensuring that the heart has enough time to relax and fill with blood before the next contraction. This mechanism is essential for maintaining a rhythmic and effective heartbeat.

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Related Practice

Textbook Question

Mark the following statements as true or false. If a statement is false, correct it to make a true statement.

Pacemaker cells lack a distinct plateau phase.

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Textbook Question

Mark the following statements as true or false. If a statement is false, correct it to make a true statement.

The plateau phase in contractile cells is due to the influx of calcium ions through calcium ion channels.

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Textbook Question

Mark the following statements as true or false. If a statement is false, correct it to make a true statement.

The repolarization phase of the contractile cell is due to the potassium ions rushing into the cell through potassium ion channels.

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Textbook Question

Mark the following statements as true or false. If a statement is false, correct it to make a true statement.

Open sodium ion channels cause hyperpolarization in pacemaker cells, which triggers HCN channels to open and begins a new action potential.

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Textbook Question

An experimental toxin makes the refractory period of cardiac muscle cells equal in length to that of skeletal muscle fibers. Predict the consequences of this toxin.

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Multiple Choice

The absolute refractory period refers to the time during which __________.

The noncontractile cardiac muscle cells that initiate their own depolarization and cause depolarization of the rest of the heart are called __________.

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