Nodal tissue is a unique type of tissue that has both muscular and nervous characteristics, and can be found at two points in the heart: the sinoatrial node (SA node) and the atrioventricular node (AV node). It is responsible for coordinating the cardiac cycle (heartbeat).

The SA node is found at the upper dorsal wall of the right atrium. It initiates the heartbeat, by sending out an excitation impulse every 0.85 seconds, causing the atria to contract.

When this impulse reaches the AV node, which is located at the base of the right atrium very near the septum, it signals the ventricles to contract by way of two large fibers terminating in the many small Purkinje fibers.

The SA node is commonly refered to as the pacemaker, because it keeps the heartbeat regular. If for some reason it fails to work properly, the heart will still beat, but irregularly. In recent years though, artificial pacemakers have come a long way, and it's now fairly easy to correct any problems.

Unlike my procrastinating self, the heart is intrinsically motivated, which is to say that it mostly directs itself, rather than having the brain control it. It is these nodes which are source of this.

Log in or register to write something here or to contact authors.