The pacemaker action potentials in the heart
A) are due to opposing actions of norepinephrine and acetylcholine.
B) are generated by the bundle of His.
C) depend on the gap junctions between the cells that make up the atria and those that make up the ventricles.
D) are due to spontaneous depolarization of the plasma membranes of modified cardiac muscle cells.
E) result from hyperpolarization of cells in the sinoatrial node.

Question

Quizplus · Accepted Answer

The pacemaker action potentials in the heart are due to the spontaneous depolarization of the plasma membranes of modified cardiac muscle cells. These cells, located in the sinoatrial node, have an intrinsic pacemaker activity that sets the heart rate. This depolarization is due to the opening of voltage-gated ion channels, mainly L-type calcium channels, causing the influx of calcium ions, which triggers contraction of the cardiac muscle cells. This process is independent of neurotransmitters such as norepinephrine and acetylcholine or specific conducting fibers such as the bundle of His.

The Pacemaker Action Potentials in the Heart