"The sinoatrial node (SA node), rarely also spelt sinuatrial node, is a group of specialised pacemaker cells that controls the rate of the heart, representing part of the intrinsic innervation of the heart."
"sympathetic nervous system: increases the firing rate of the SA node and thus increases the heart rate"
"parasympathetic nervous system: decreases the firing rate of the SA node decreases and thus decreases the heart rate"