01-15-2011, 07:28 PM
The action of acetylcholine after binding to muscarinic receptors on the SA node is to
A) open K+ channels, causing hyperpolarization and a decreased rate of spontaneous depolarization
B) close K+ channels, causing depolarization and and increased rate of spontaneous depolarization
C) open Ca2+ channels, causing increased Ca2+ entry and a stronger contraction
D) close Ca2+ channels, causing decreased Ca2+ entry and a faster rate of spontaneous depolarization