How does cardiac action potential duration compare to skeletal muscle and nerve?

How does cardiac action potential duration compare to skeletal muscle and nerve?

• A. Shorter than skeletal muscle and nerve
• B. Similar to skeletal muscle and nerve
• C. Greater than ten times longer than skeletal muscle and nerve
• D. About twice as long as skeletal muscle and nerve

Answer: (C)

The main idea is that cardiac action potentials are much longer than those in skeletal muscle and nerve, and this comes from a plateau phase that keeps the cell depolarized longer. In ventricular (and atrial) heart muscle, after the initial depolarization, L-type calcium channels open and sustain a calcium influx while potassium channels slowly help return the membrane toward resting potential. This creates a phase 2 plateau that can last hundreds of milliseconds. Because of this plateau, the overall action potential duration in cardiac cells is about 200–300 ms in humans, far longer than in skeletal muscle (roughly 2–5 ms) or nerve (about 1–5 ms). The prolonged duration also prolongs the refractory period, preventing tetanus and allowing the heart to fill between beats.

The main idea is that cardiac action potentials are much longer than those in skeletal muscle and nerve, and this comes from a plateau phase that keeps the cell depolarized longer. In ventricular (and atrial) heart muscle, after the initial depolarization, L-type calcium channels open and sustain a calcium influx while potassium channels slowly help return the membrane toward resting potential. This creates a phase 2 plateau that can last hundreds of milliseconds. Because of this plateau, the overall action potential duration in cardiac cells is about 200–300 ms in humans, far longer than in skeletal muscle (roughly 2–5 ms) or nerve (about 1–5 ms). The prolonged duration also prolongs the refractory period, preventing tetanus and allowing the heart to fill between beats.