Cardiac muscle cells are typically characterized as what in relation to pacemaker cells?

• A. Followers that require pacemaker cells to stimulate them
• B. Leaders that pace the heart themselves
• C. Independent and self-sufficient
• D. Contract only when ischemic

Answer: (A)

Cardiac contractile muscle cells do not generate their own rhythm; they rely on the conduction system’s pacemaker cells to start each heartbeat. Pacemaker cells in the SA and AV nodes spontaneously depolarize and send impulses that propagate through the heart, triggering the contractile cells to depolarize and contract. Because these muscle cells respond to, rather than initiate, electrical activity, they are best described as followers that require stimulation from pacemaker cells to pace the heart. They do not pace themselves, they are not independent and self-sufficient, and they don’t contract only during ischemia.