Regulation of Heart RateSpontaneous depolarization occurs at SA node when HCN channels open, allowing Na+ in.
Open due to hyperpolarization at the end of the preceding action potential
Sympathetic norepinephrine and adrenal epinephrine keep HCN channels open, increasing heart rate.
Parasympathetic acetylcholine opens K+ channels, slowing heart rate.
Controlled by cardiac center of medulla oblongata that is affected by higher brain centers