<Tr> <Th> FMA </Th> <Td> 9477 </Td> </Tr> <Tr> <Td_colspan="2"> Anatomical terminology (edit on Wikidata) </Td> </Tr> <P> The sinoatrial node (SA node), also known as sinus node, is a group of cells located in the wall of the right atrium of the heart . These cells have the ability to spontaneously produce an electrical impulse (action potential; see below for more details), that travels through the heart via the electrical conduction system (see figure 1) causing it to contract . In a healthy heart, the SA node continuously produces action potential, setting the rhythm of the heart and so is known as the heart's natural pacemaker . The rate of action potential production (and therefore the heart rate) is influenced by nerves that supply it . </P> <P> The sinoatrial node is a banana - shaped structure that varies in size, usually between 10 - 30 millimeters (mm) long, 5--7 mm wide, and 1--2 mm deep . </P>

Which of the following is often called the pacemaker of the heart