Sinoatrial node is influenced by nerves that supply it. 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. The SA node is located in the wall (myocardium) of the right atrium, laterally to the entrance of the superior vena cava in a region called the sinus venarum (hence "sino-" + "atrial)". It is positioned roughly between a groove called the crista terminalis located on the internal surface of the heart and the corresponding sulcus terminalis, on the external surface. These grooves run between the entrance of the
Sinoatrial node slowly). These channels allow a flow of calcium ions (Ca) into the cell, making the membrane potential more positive. Phase 0 This is the depolarisation phase. When the membrane potential reaches a threshold value (around -20 to -50 mV), it begins to rapidly depolarise (become more positive). This is mainly due to the flow of Ca through the L-type calcium channels, which are now fully open. During this stage the T-type calcium channels and HCN channels deactivate. Phase 3 This phase is the repolarisation phase. This occurs due to the inactivation of the L-type calcium channels (preventing the movement of