Sinoatrial node Sinoatrial node 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)
Sinoatrial node (in particular T1-T4). These nerves release a neurotransmitter called noradrenaline (NA). This binds to a receptor on the SA node membrane, called a beta-1adrenoceptor. Binding of NA to this receptor activates a G-protein (in particular a G-Protein, S for stimulatory) which initiates a series of reactions (known as the cAMP pathway) that results in the production of a molecule called cyclic adenosinemonophosphate (cAMP). This cAMP binds to the HCN channel (see above). Binding of cAMP to the HCN, increases the flow of Na and K into the cell, speeding up the pacemaker potential, so producing action potentials at a quicker