Which cells are pacemaker cells?

Which cells are pacemaker cells?

• A. Sinoatrial and atrioventricular nodes
• B. Atrial and ventricular contracting myocytes
• C. Purkinje fibers
• D. Bundle of His

Answer: (A)

Automaticity in cardiac tissue is what creates the heart’s rhythm. The cells in the sinoatrial node act as the primary natural pacemaker, spontaneously depolarizing and setting the heart rate. The atrioventricular node also has automaticity and can take over if the SA node fails, though at a slower intrinsic rate. These nodal cells are different from contracting myocytes, which are the atrial and ventricular muscle cells that produce force but don’t pace the heart on their own. Purkinje fibers and the bundle of His are fast-conducting pathways that quickly relay impulses to the ventricles; they don’t normally set the rhythm. So the pacemaker cells are the ones in the SA node and the AV node.

Automaticity in cardiac tissue is what creates the heart’s rhythm. The cells in the sinoatrial node act as the primary natural pacemaker, spontaneously depolarizing and setting the heart rate. The atrioventricular node also has automaticity and can take over if the SA node fails, though at a slower intrinsic rate. These nodal cells are different from contracting myocytes, which are the atrial and ventricular muscle cells that produce force but don’t pace the heart on their own. Purkinje fibers and the bundle of His are fast-conducting pathways that quickly relay impulses to the ventricles; they don’t normally set the rhythm. So the pacemaker cells are the ones in the SA node and the AV node.