Which feature is characteristic of an action potential at the SA node?

• A. Inhibition by acetylcholine
• B. Rapid repolarization
• C. Spontaneous depolarization
• D. Stable resting membrane potential

Answer: (C)

Verified step by step guidance

1. Understand the role of the SA node: The sinoatrial (SA) node is the natural pacemaker of the heart, responsible for initiating the electrical impulses that set the rhythm for heartbeats.
2. Identify the characteristic feature of the SA node: The SA node is known for its ability to spontaneously depolarize, which means it can generate action potentials without external stimuli.
3. Explore the concept of spontaneous depolarization: Spontaneous depolarization refers to the gradual increase in membrane potential that occurs in pacemaker cells, leading to the threshold potential and triggering an action potential.
4. Differentiate from other features: While acetylcholine can inhibit the SA node by slowing down the heart rate, and rapid repolarization is a feature of other cardiac cells, the SA node's unique characteristic is its spontaneous depolarization.
5. Clarify stable resting membrane potential: Unlike other neurons or muscle cells, the SA node does not have a stable resting membrane potential, which allows it to continuously initiate action potentials.