Pacemaker cells isolated from the SA node generate action potentials at approximately how many beats per minute?

• A. 120 beats per minute
• B. 40 beats per minute
• C. 100 beats per minute
• D. 60 beats per minute

Answer: (C)

Verified step by step guidance

1. Understand the role of pacemaker cells: Pacemaker cells in the sinoatrial (SA) node are specialized cardiac cells responsible for initiating the electrical impulses that regulate the heart's rhythm. These cells generate action potentials spontaneously due to their unique ion channel properties.
2. Learn the intrinsic firing rate of the SA node: The SA node's pacemaker cells have an intrinsic firing rate of approximately 100 beats per minute under normal conditions, which is the heart's natural rhythm without external influences.
3. Consider autonomic nervous system modulation: The actual heart rate in a living organism is often lower than 100 beats per minute due to parasympathetic nervous system activity (via the vagus nerve), which slows the heart rate to around 60-80 beats per minute at rest.
4. Compare the options provided: Among the choices given (120, 40, 100, and 60 beats per minute), the intrinsic firing rate of the SA node aligns with 100 beats per minute, which is the correct answer.
5. Conclude with the physiological significance: The SA node's intrinsic firing rate ensures the heart maintains a consistent rhythm, which is crucial for effective blood circulation throughout the body.