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

14. The Autonomic Nervous System

Introduction to the Autonomic Nervous System

Anatomy & Physiology

14. The Autonomic Nervous System

Introduction to the Autonomic Nervous System

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Multiple Choice

Which statement best describes phase 4 of the action potential in sinoatrial (SA) node cells?

It is the rapid repolarization phase caused by potassium efflux.

It is the initial rapid depolarization due to sodium influx.

It is the spontaneous depolarization phase that determines the heart's pacemaker activity.

It is the plateau phase maintained by calcium influx.

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Verified step by step guidance

Step 1: Understand the phases of the action potential in sinoatrial (SA) node cells. The SA node is the heart's natural pacemaker, and its action potential is unique compared to other cardiac cells. It consists of three main phases: phase 4 (spontaneous depolarization), phase 0 (rapid depolarization), and phase 3 (repolarization).

Step 2: Focus on phase 4 of the SA node action potential. This phase is characterized by spontaneous depolarization, which is crucial for the pacemaker activity of the heart. During this phase, the membrane potential gradually becomes less negative due to the activity of specific ion channels.

Step 3: Identify the key ion channels involved in phase 4. The 'funny' current (If), carried by sodium and potassium ions, plays a major role in initiating the depolarization. Additionally, transient calcium channels (T-type Ca²⁺ channels) contribute to the gradual depolarization as the membrane potential approaches the threshold.

Step 4: Compare the descriptions provided in the problem. The correct description of phase 4 is 'It is the spontaneous depolarization phase that determines the heart's pacemaker activity,' as this phase is responsible for generating rhythmic electrical impulses that regulate the heartbeat.

Step 5: Eliminate the incorrect options. The other descriptions refer to phases of action potentials in different types of cardiac cells or phases other than phase 4 in SA node cells. For example, rapid repolarization due to potassium efflux occurs in phase 3, and the plateau phase maintained by calcium influx is characteristic of ventricular myocytes, not SA node cells.